IATA would be a good place to start.

lambaste them (politely) on Twitter and FB (and other social networks they have a presence).
It was the only way Air Asia would even respond to me.
If it worked for Air Asia it should work for a slightly higher quality carrier like Malaysian airlines

Not sure invisable agent about the "higher quality carrier bit" I have travelled frequently over the years with both MAH and airasia and I think that air asia have surpassed MAH. By a long way.
I will use this reply to warn anyone travelling in the future with Malaysian airlines to be very carefull regarding excess baggage. Unlike air asia you cannot upgrade your baggage past 20kg with Malaysian airlines. You just have to pay excess baggage at checkin. I had travelled from OZ to KL with Airasia and upgraded to 40kg for a mere $40.
Upon changing airlines at KL to avoid an 8hr stoppover I checked in with Malaysian airlines to continue onto PP. I had done my homework as I had 18kg excess baggage and Malaysian airlines stated on their website that excess baggage would be charged at
1.5% of the normal ticketed airfare for every kilo of excess. As my Ticket cost about $120 and was considered normal as it was not a promotional fare I calculated that I was up for about $32 for the 18kg which seemed reasonable. I was informed at checkin that the fee for my 18kg would be 452myr or $150.
They refused pointblank to accept my version of their website etc.. and made no attempt to provide me with any information to the contrary. Time was running out to catch my flight so I paid along with advising them that a complaint would be lodged.
I have since sent emails to their disputes section but these have been ignored. The guy next to me was hit with $400 due to the same bullshit...
Malaysian airlines have always been difficult but now have just become common theives. I guess thats why everone flies with airasia now and that's why the flight from KL to PP had nearly more cabin crew than passangers.... So be warned
I did look up IATA (thanks Alphons) seems I have to write a hard copy letter to the Malaysian branch of IATA. As there was no email contact..shall give that a try. Next time I will endure the 8hr stoppover to continue on with air asia just to avoid giving MAH one cent... It cost $30 more to send my 18kg than my god damn flight cost... what a joke.

Ya gotta love social networks

robshep56 - click onto this page mate.
I posted some of your text - https://www.facebook.com/malaysiaairlines

Hi Expat Advisory - after reviewing our baggage page, we believe you have mistaken our Excess Value Declaration charges which differs from our excess baggage charges. However, if you like to raise a complaint, kindly send your flight details to socialmedia [dot] team [at] malaysiaairlines [dot] com and we will forward it to our Customer Care team for further action.

Thanks admin... I have actually avoided social networks so not able to veiw the link as yet. I shall join facebook soon as to vent my displeasure with Malasia airlines. I have written a letter to the Malaysian Branch of IATA regrding my complaint and am about to send my complaint to the socialmedia team of Malasia airlines that responded to your entry... Don't know where they get anything about excess value declaration out of all this. Talkin to a mate the other day who was sung also and filed complaints and it seems that excess baggage is actually calculated on business class airfares. None of which are displayed on the website. Well I guess it was nice to know that while I travelled with my knees stuck up under my chin in cattle class my 18kg excess baggage was enjoying the comforts of business class.......speachless

Where were you reading the baggage rates on MA's website?

I can only find this:
http://www.malaysiaairlines.com/my/en/book-and-plan/baggage/checked-bagg...

And the only 1.5% on there is for excess value declarations.

It's rather vague on the rate for excess weight.

"A charge at the appropriate journey rate per kilogram will apply for any baggage carried in excess of the free baggage allowance as above."

Whatever that means.

Yeah... And started with the excess baggage link. Everything on the Malaysia website regarding excess baggage is a tad vague. I do have a screen print I saved that does actually say 1.5% of the normal highest ticketed price ( econamy class fare ) for every kilo over weight for international flights. It does mention that this can vary depending on the destination country.. but I never could find this info out, so it is either not there or very well hidden. I could send you my screenprint if you supply me with your email address...cheers Rob

Don't worry about it. I'm flying Thai now.