ask them if they can re write your account coz they can ! The store has to achieve a target each Saturday on there collections and its done in percentage { ie if they need £200 pounds to reach a target ) if you owe 180 they can re write your account and clear your debt thus clearing 180 off there debt ! they are under great pressure to achieve these goals so tell them you can pay one weeks payment only .You wont get any money back for what youve paid already if you return the stuff .