ebay final value fees

[allen63b]

I am having some difficulty with ebay regarding their final value fees.
To put it simply I sold a car but on two occasions the deal fell through. They say they have given me a FVF but because I pressed the reverse key they took the fee back off me!
I don't recall clicking the reverse option and can't see how they can charge me three times for the same item.
Has anyone any idea of how I can get my money refunded as all I seem to get is a standard reply.
Are there any regulators I can contact?
Thanks in advance
Allen