Vodacom refusing to cancel their line yet my contract lapsed

Vodacom is my current worst nightmare, i had a 24 months LTE contract which lapsed in November last year, for the contract i was paying R299 and there after they changed it to month to month without my consent, they started billing me R600 per month, i paid them then upgraded to fibre with them and asked them to cancel the home LTE, instead they kept both lines open and i haven't been paying them for the LTE but they refuse to cancel the contract now saying it's in arrears therefore it will continue pilling up every month, i have been in contact with them since the beginning of this year to rectify this issue but still no help, the move me from pillar to post when i call them, my bill is sitting at more than R4000 now they still don't want to cancel their contract yet I'm not using it. Very frustrating as at this rate their account will go above R50 000 since they are refusing to cancel it.