Vodacom Violating single mom

I downgraded my Vodacom package in Feb 2019 online and the I Phone 8 I received was faulty. I then went to Vodacom Canal Walk who send the phone in to confirm the out of box guarantee. Happy to say they replaced my Phone in the week before the 16th of March. I received an astronomical account and contacted them on the 10th of April to find out what was going on. After being on the phone for what seemed like hours, they informed me that they by mistake cancelled my original down grade and took it back to the old contract and on top of that also charged me a device fee. Being a single mom and not at all able to afford this (I also explained this to them) they promised me that they will correct this at the end of April and give me a big credit on my account. Guess what? following up this morning this was not rectified! I spoke to Patricia on the customer care line who said she is a supervisor and promised that she would phone back by three today, but did not promise to rectify this. Again an account which I can not afford. Vodacom you are violating my consumer rights and taking advantage of me as a single mom. Your mistakes are costing me a fortune.