VT - Collection Charge

[SallyBell]

I VT's my agreement a couple of months ago. I did not sign the forms they wanted me to and acted on the advice from this site. I wrote the letter using the template from this site also damages, excess mileage and collection charges. I have finally, after being ignored for so long and refusing to answer many phone calls from them, received a final response letter. I will agree to pay the mileage charge as I do not mind this as the mileage was above the agreed amount but I do not agree to paying the collection charge. They say that despite what I say in my letter to them some clauses remain enforceable and they are entitled to levy a charge. Is this correct? Thanks