Return car in excellent condition mercedes

[clydebonnie]

Mercedes collected my car at the end of lease, the car was in immaculate condition and below the miles allowed, yet was sent a bill for £700, I told them no way I have delt with them having several cars over the years, they reduced my bill by 20% as a good will gesture, I ignored them and have just got a letter from Mortimers solicitors Essex say they are claiming the money on behalf of Mercedes and the bill has gone back to the original fee, I strongly want to contest this as I took so much care to return car in the best condition, I feel I am being scamed