Black horse VT liability costs

[Guest]

Hi i am needing some advice here. So i won the battle to VT with black horse. After several letters they finally came and picked the car up, without me paying the £75 collection fee (although ofcourse they say its outstanding). But anyway during the VT they said i was liable for £568 left in warranty and gap fees and this amount was not included in my total amount payable and so i understand i was liable. So i called them to pay once the car had gone, meanwhile they claim i am behind with the monthly agreement payments since i notified them of VT, i cancelled the DD ofcourse. So i call to pay my liability figure and few days later letter comes and says that payment has been used to clear my 'arrears' for the monthly payments! So they have taken my mo money and used it to pay for something else completely! How do i approach this one?? Any advice would be much appreciated, i am beyond exhausted with them now it's a ridiculous constant battle.