MTN billing shady practices

For some reason they were trying to charge me for an additional month on a 24month contract citing i need to give 30 days notice to cancel the contract? please explain to me how 30 days notice means i owe you an extra full payment on the account when the sim card was converted to a Pay as you go a month before. additionally i logged the request to cancel the contract more than a month before it was and it was them who took forever to action it.