Worst customer service ever

I've taken a wifi LTE contract with Cell C and it runs at snails speed!!! Two days later I contacted them to let them know I am not satisfied with the product and they said they will investigate. A week later they say a technician can to my area and it's running fine at 2.1mbs!!!! I was promised up to 150mbps and this is barely running at 1% of that and they say they are happy with it. Told me to screen grab the screen of the running speed to which I did and up til now no response. I want cell c to take their **** device and service back or this will go public and reported to cpa and ncr. There's no way I am going to be paying R500 a month for unsatisfactory service and to be treated like dirt. Please do NOT sign up with this network if you want good service or network because that isn't going to happen.