Unable to cancel membership & Unauthorized Debits

I canceled my membership in Sep 2020. The continued to attempt to debit my account. I had to stop debit order to stop them taking money from my account. I continued receiving SMS accusing me of non payment. I sent a mail again on 20 Jan 2021 and attached my previous from mail that I gave notice notice. I still get SMS telling me I am not paying. 8 March I received a SMS saying I have been handed over to Attorneys for collection.