Telkom debiting large amounts of money but cutting off signal

My husband did an early upgrade on his contract, the salesman that helped him showed him he was only going to pay an additional amount of about R400 which would have worked out to R2400 a month until December. Telkom has been debiting +- R3800 a month and cuts off my husband's signal so the phone is basically not operational. When he calls in to try and resolve it the agents try and insist he pays at additional +- R900 for costs that was not disclosed and has told him that his network will be cut every month until the amount is paid up until December. They also don't want to cancel the contract they demanding he pays the full contract amount.