Invalid 30 Days' Notice Period and Rude Cancellation Consultant

I called MTN to cancel my contract (Samsung S20 Ultra + 50 minutes for 36 months) that has expired on 03/05/2023 and i get told by a rude Cancellation Consultant that there is 30 days' notice period. For what reason is this 30 days' notice as the 36 months contract with MTN has lapsed. I called in April and was told that i should contact a day after expiry of contract as they can't cancel the contract. I could have made the 30 days' notice period in April. This contract is for a cellphone and 50 minutes. I will not be paying for an additional month of R799.00 for a cellphone that I have completed paying for 36 months as per contract. No where on the signed contract does it stipulate a 30 days' notice. MTN cancel this contract number *** with immediate effect. The billing for 17th of April 2023 minutes loaded as per my billing cycle will be the last deduction to be made by 31 May 2023. Listen to my call at 16:45 that i made spoken to the Rude Cancellation Consultant who put me on hold without reason.