BMW Financial Excess Mile Charges - Do i have to pay?

Hi All, BMW Excess miles charges after voluntary termination of my agreement...do i have to pay them?

I look back at my original agreement and it says

You have a right to end this agreement. They will then be entitled to the return of the goods (obviously giving the car back) and to half the total amount payable under this agreement (which i have paid). If you have already paid this you will not have to pay anymore. You will have to return the vehicle and pay any arrears and any other sums which have become payable under the agreement before the termination (including any excess mileage charge).

We signed this agreement but i am reading so many websites and forums saying they can threaten you but cant do much more than that.

Anyone signed something similar and then refused to pay and been ok?