I never requested for an open line and i was not informed

I am writing this message with so much anger and disappointment , I took out a small contract last year for my daughter which was supposed to be less than 250 every month and I was not informed about any open line nothing what so ever , the first two months the bill was normal and came December I got a bill shock of 800 as if am paying for an iPhone , I ignored the bill thinking maybe this is due to the last invoice of the WiFi which I previously cancelled , to my surprise this happened again in Jan and that when I called MTN I was informed of the open line which I was not informed about when I took out the contract I got so mad and requested for the open line to be closed with immediate effect and that was done I also removed the sim from my daughters phone and boom the same thing happens this month another bill shock, I logged an SR and the response was the SR was closed with no comment and I should go where I took the contract???? Like really what’s that am I not escalating to MTN I then called directly spoke with a very so called service consultant who refused to give me her surname but gave me her name which is SESANI, that agent is extremely rude and guess what she hung up on me just because I requested to speak with the supervisor after holding for 20 minutes she hung and didn’t bother to call back, MTN I want my extra 500 which was debited monthly in my bank as that’s not what I agreed upon too if the open line was generated by your partners you’ll will deal with them but I want my money from you’ll My ID number is ***

Get the matter resolved and am demanding an apology from the agent who rudely disconnected my call