Unfair billing and charges, faulty tablet and mode

I have been charged the incorrect amount for my internet usage. The tablet is faulty and no one is assisting me, they have delivered a wrong sim card that came with the tablet and they dont care about it. The moderm is not working is february and no one is asstisting me until I send it to Mall of the North for repaires but every month they are billing me rediculous amounts. They have twisted the phone number with another person's gadgets and they charge me rediculous amounts and they force me to pay. I am stressed and suffocating when I think about the way Cell C is treating me. I want to cancel these contracts with immediate effect please