Being charged for services not rendered - incorrect invoicing.

I canceled my account on 8 January 2021. Got confirmation from Telkom that the last day will be 8 February 2021. On 10 February 2021 received an invoice with charges for services from 9 February to 8 March.

Phone in twice to have the invoice correct. Telkom Billing refuses to correct the invoice or let me speak to a manager.

Got the final invoice which is also incorrect because of the previous incorrect invoice. If the invoicing is corrected Telkom actually owes me money.

Now a debt collection agency phones me every day.

Shall I lay charges of ***** against Telkom of drag Telkom through the Small Claims Court?