Debits for account that was paid up

I did my glasses via dit optometrist last year April and had 8 months to pay off via debit I received glasses May/June and notify them am not seeing properly with it no one attended to my call logged in October I decided stop my debit and have a respond from them was suppose to end agreement November but because stop debit I ended December. My glasses were picked up and sorded before December. I made my last payment December and no one contact me regarding any payment January they try to debit and was unpaid I can't act them and query the debit they said it's because I missed payment October explain that I paid it December. The following mth they try again and was told to send bank statements. Why mst I send statement if I have to pay and who are reliable for debits they run every month that gets return it was not my fault that the glasses were not fit and why did they only respond when payment was stop August and sept I paid for query that was already logged they mst stop debiting my account because now they are trying every month and debits returned. Am not owing them for work poorly done on they side. They mst stop debiting my account