Cell C not prepared to assist with poor signal. Pathetic service!

I convinced my mom to migrate from Vodacom to Cell C due to poor customer service on 31 Aug 2018. This was after I purchased a prepaid sim card for her and tested it for a month with no issues. A week after migrating the problems with the voice and data signal started. We have been in contact with Cell C numerous times and they have admitted that there is a poor signal...and that is in a residential area where there are a few estates en 2 high schools surrounding her. They can't guarantee when they can improve/sort out their issues at all due to their budget! Well, it is not in my budget any more to keep on paying for this contract without getting a service. Cell C can't expect me to pay a settlement fee to cancel the contract. It is not fair as the problem din't exist in the beginning and now due to their problems they wan't to shift the costs to me. In the mean time I had to buy a mtn sim card and there are no signal issues. The last advice that the CELL C consultants gave us was to search for a network and choose MTN but we just get an error message indicating that the sim card doesn't allow that. Cell C confirmed that the sim card can migrate to MTN and after telling them a few times that I am not able to do it for my mom, not even on another cellphone, they are not able to offer other help. So Cell C, do you mind if I just stop paying as you just stopped rendering a basic service??????? This is a serious matter as my mom is 80 years old and needs to communicate in case of emergency. Why do I have to spend money buying airtime from MTN if I have a contract from you providing what my mom needs?