Cell-C has a ****ty service & cannot be trusted, I upgraded to 50Mbps but I receive even less than 20Mbps connection

I keep calling Cell-C for help and I haven't heard anything from them and I have sent them countless emails of what they asked for and called them several times for updates and still they are not willing to help me. If they do not improve my connection, I would like a refund since I am paying for a very poor service. I should be getting 50Mbps and now I am getting Fiber connection of less than 20Mbps and this is a total rip-off. A week ago I had a good connection and now suddenly it has gone down and its buffering and Wi-Fi is showing one bar connection and I can only stream 360p quality which is ridiculous since I recently upgraded because I wanted to receive 4K streaming quality. I will really cancel the contract if I keep getting this stupid poor quality connection and I am paying a lot of money for this nonsense service. Cell-C said they are going to investigate and the week has passed and I haven't heard anything from them and the connection is still bad and getting worse. I am going to migrate to another service provider on Monday if I don't get help by this weekend.