MTN

MTN no: ***/ we had a data contract with MTN since 2012, never renewed the contract, therefore it should be a30 day notice period. we cancelled the contract on 31 July 2020 via e-mail given them 1 calendar month notice. MTN then send me a message that I must phone in to cancel contract, received a mail to forward my ID no. etc. they still bill me for the service which i don't use and deduct money from our account. how can i resolve this issue?