BAD SERVICE AND HARASSING CALLS

I ordered Goods from them last year. The arrangement between us was to take Debit orders for the goods until its paid off.They called me in lock down to inform me that my accounts is behind and i asked them how because i did not stop my debit order they kept telling me that i cancelled my debit order i asked them to send me the proof were i cancelled it and they cannot give me any proof. I am getting phone calls everyday and its not even my fault that the accounts is behind i told them to take X Amount per month to get the account up to date but as soon as the debit order goes off they phone me to ask when am i going to pay. I AM OVER HOMECHOICE they don't know what they doing .The one person tells me they will inform his accounts departments that is not my fault and the other person is so rude and if you give it back to them they put the phone down in your ear.WHAT KIND OF BUSINESS ARE YOU RUNNING. GET SOMEONE TO CALL ME THAT WILL BE ABLE TO RESOLVE THE PROBLEM.