CELLPHONE CONTRACT CANCELLATION

I am very unhappy with the level of service from mtn it was easy for them to give me a cell phone contract but now that the period has ended they taking their time to cancel my contract and it ended last year 2020 they still keep sending me invoices, please cancel my contract even at the eastgate store I got no help and when you call you hold for hours with no answer I already sent a query on your customer care email my reference is *** received it on the 23rd of January and it says you resolve queries within 8 working hours.