Contract Cancellation Penalty

I am under an MTN Cellphone contract that is about to expire on 11 June 2024, and I made an effort to call customer care on the 03 May 2024 to cancel my contract because I was notified that i should give a 30 Day notice of cancellation, and i spoke to Nzuza (Call centre) which he promised that someone will call me back, but nobody called me , until the 06 May 2024 i called the customer care line 135 and spoke to Wandile (Call centre agent) and he told me that Nzuza didnt make any notes on the system that i should be called and he told me that he will process everything on under my name for cancellation and even asked be ridiculous questions like why do i need to cancell the contract, can they still keep me as a customer. and I started getting annoyed because i felt like he was not listerning to me that i want to cancel everything about the contract and I Dont want any month to month billings no more, he allowed me to think that he is sending the notification for cancellation until after an hour of speaking to him he told me that I phoned too early the date of calling for cancellation is on 11 May and I should call on 10 th May 2024 becuase the 11th May 2024 falls on saturday and they dont operate on weekend, the he promised to call me on the 10 May 2024, but he also failed to call me on the 10th May 2024, then I called the customer care on 13 May 2024 and spoke to NCwado, also from customer call for him to tell me that there is nothing he can do because i failed to call in the right time to cancell therefore the only option is to call again next month on the 11 June 2024 but they will keep billing me and I told him that, this is unfair your staff members failed to call me as promised and they failed to explain to me that they cannot cancel my contract in time, therefore i am requesting a clear answer as to what to do in this matter as i still want to cancel the contract and not billed after the contract expires on 11 June 2024 because i have been a loyal customer by paying my contract full term.