Excess mileage charges on voluntary termination

[LolB]

I wrote to Mercedes requesting a voluntary termination of my finance agreement. I signed the form they sent me, but deleting the acceptance of excess mileage charges and highlighting that I had done so in the covering email. Having inspected and collected the vehicle they sent me a bill for two damaged tyres (which I accept) and excess mileage. I wrote accepting the damage charge but not the excess mileage charge. They responded saying that the Consumer Credit Act allows them to include any over mileage when determining what is 'not reasonable' upon the car's return and referring to a term in my agreement under the heading of 'Excess Distance'. I am not at all sure that I received a copy of the full terms and conditions of the contract when I bought the car as I am reasonably well organised and do not have a copy on file. I have requested a copy of the T&Cs on three occasions and have not received them. However, I cannot prove that I never received them in the first place so assume it is not worth using this as an argument. I wrote again (following a Legal Beagles template - thanks) stating that the vehicle had met all the vehicle condition terms (full service history etc), that it was in reasonable condition and that they had provided no evidence of damage caused by the excess mileage. I have now received a further letter saying that they have considered my claim and repeating that the Consumer Credit Act allows them to include over mileage etc. and referring to the the term in the agreement. They acknowledge that I crossed out reference to excess mileage charges but state that this does not negate my contractual obligation and that, as excess mileage is a condition of my signed agreement, they retain the right to raise a charge for this. They end their letter by stating that this is their final decision but if I am unhappy I have the right to refer the matter to the ombudsman. I assume therefore, that there is no point in arguing further with them so my question is, is it worth referring the matter to the ombudsman? (I found an example of a similar case where the ombudsman found against the customer). Secondly, if I do refer to the ombudsman, do I have to pay the money and then claim it back if the ombudsman finds in my favour, or should I write advising Mercedes that I intend to refer the matter to the ombudsman and that I am therefore withholding payment pending their decision? Is there any other option open to me? Any advice greatly appreciated.