Bad Service from IS :(

I have 100+ devices on a mobile network, I decided to use IS as a service provider using the shared APN platform, I contacted them as was provided Shaka Vilakazi to assist me in getting started, I explained to them that I need a low-cost solution, I was prepared to pay R1000 pm for all sims for data, this I was promised to be the case, at first the told me I will pay R10 per sim per month, data will be billed separately, I did not mind because their rates were reasonable, 15 Aug 2019 I had a surprise bill of R2,941.73 I emailed them immediently and I did not received any answer, this continued till Dec where I sent them an email to cancell the service as I felt mislead by them, when I wanted more sim I was told a sim cost R100 each, this was not explained to me, on occations I would get questionable data high data usage > 500MB from devices which only report 100 bytes every 20 sec at most, I queried this aswell and I was given vague answers, I have been asking them since to cancel this service as I am not happy with them and they are refusing, they are now ignoring my emails of cancellaton, initially, they would close cases without informing me, I do not want this service anymore I want my sim cars on pre-paid.