Matrix bullies

I am beyond frustrated with this company. I have cancelled my subscription in May, paid the settlement provided by them. Two months later a debit order went off (which I reversed) for an outstanding balance. I have sent numerous emails requesting feedback on this matter. Not one email reply. Now I have received a final demand email stating that If I don't pay, a summons will be issues to recover the fee and the cost will be for my account. If you pay a settlement amount for something, it means your account/agreement is paid in full. Does it not? I don't think I should be held liable for any further cost, as I have paid the settlement amount provided by them.