Incorrect order delivered, correct order remains undelivered more than 1 month later

I signed up online for the Sep data deal in mid Sep. Delivery took place early October and it was a cellphone instead of a modem that I signed up for. I reported it the next day and did more than 6 follow up calls since then each lasting more than 15 minutes. Every consultant assured me that they have escalated the call to the correct department and that someone will call me to resolve but more than a month later nothing has been done. To make matters worse, I receive an invoice of R580 when I signed up for a deal of R130. All communication channels have been exhausted. I need this resolved ASAP. Better yet cancel the entire contract because I cannot deal with such incompetence. I will be putting a stop order at my bank to prevent any debits.