Account incompetence

Cant give them a zero, not permitted. Paid my account the 27th of September like I always do, via eft. Nothing changed. Overpaid the account, also per usual. Now I get hounded by phone and email by Nation Wide Debt Collection, for overdue account. According to Woolworths I didn't pay in September... this is after they cancelled my card in April because of supposed *****... the ***** was a online order which I cancelled because the delivery date was 12 weeks away...If my credit rating is affected because of this, there will be hell to pay..