This was not a Section 75 claim if that's what you mean. My card is a BA badged American Express card and I simply invoked the standard charges dispute process.
The pure online process wouldn't load (too many charges being disputed), so I disputed the charge with an operator via the Chat function, The key part was that I had already discussed the matter with Malaysian, and that they had refused to refund me, despite them having cancelled my flights.
Since I had already sought, but failed to get a resolution from Malaysian, the amount I had paid was refunded almost immediately, although I was told that if Malaysian were able to demonstrate that the terms and conditions of my flights allowed them to cancel the flights without refunding me, the refund could be reversed.