MTN is ******** me

My contract with MTN ended on the 01st September 2021, but they keep sending airtime and invoices to me for the prepaid contract I did not agree to, I emailed them to cancel the contract they do not reply to my mails, I go in-store to MTN Fourways mall they tell me they can't cancel in the store I have to call the call center, how outrageous is that you take a contract in store but you can't cancel ....I am really disappointed with the service.