Feeling bul**** by a service provider desperate who seem desperate to keep Clients

I've had the 24 month contract with cell c from June 2016 to May 2018. in April 2018 they called me for an upgrade and I made it clear with them that I would like to cancel my contract when it so no upgrade or extension whatsoever. I was told to give 30 day notice I called the cell c Call center to at end of April 2018 to give this notice and confirmed with them at the end of the call whether is my notice through the call valid or what other steps i still need to take and was told by the agent that it is valid and need not do anything else as the contract will be cancelled come end of may 2018. still got more calls in May 2018 for upgrade and declined and told them that i've put in the notice for cancellation. come June 2018 the contract is still not cancelled and was asked to pay for a further month this time though the email. asked to be sent the statement that reflects the 24 months invoices and payments made regarding this contract to confirm that the contract has not ended but was only send a link that gives me assess to one few last months statements. Reversed the june payment while awaiting for this matter to be resolved. They still continued not to cancel my contract through to july and now have sent aonther invoice for July period (3 months after giving them notice to cancel the contract). My Question: is it fair that Cell c is "forcing" me to stay with them even after i made it clear that i do not want to. are they desperate that much for clients? why not block my number until june dispute is resolved even after i told them to discontinue it? Why not even listen to the only two call that i made in the month of April to confirm my claim instead of sending me agents that each and everyone of them denies knowing about my notice to cancel the contract. why not make notes on the clients profile for the next agent to know about the client before calling them. Is it *********** staff or a big company trying to bully a small until he complies and stay with them?