Cell C Double charges after contract expires

I had a 20 gig (5g anytime and 15g nightsurfer) contract with Cell C for R99 a month that expired in March. My understanding was that at the end of the contract I had the option to do an upgrade or just continue on the R99p/m 5g+15g package I was on, on a month to month basis. I suddenly find they have more than doubled the monthly payment to R209p/m and their excuse is because I no longer receive the discount??? At no time did Cell C contact me to advise me that my monthly fee would now double in price. This is disgusting and basically boils down to theft in my opinion. I am trying to get hld of someone to sort it out but have been on hold so many times for over 20 minutes at cost to yself, that I cannot continue. I was told by one call centre agent that I will have to go through to cancellations department to stop this and cancel my account but this will take until the end of may and I will therefore get a 3rd double debit. I could reverse the debits but then Cell C will have my impeccable cr record black marked, so are basically holding me hostage and squeezing every cent they can. Disgusting Cell C.... disgusting!!