Turkcell Superbox Internet Speed Is Below 1 Mbps and My Problem Is Not Solved

I am using Turkcell Superbox, but my internet speed is not even 1 Mbps. I had the same problem before; I call customer service, they do something to the modem, and the internet works properly for one day. However, the same problem continues on the second day. I feel like I'm stuck in a loop where nothing gets permanently fixed. Despite paying a high monthly fee, I am not getting the service I was promised. My current internet speed is 0.60 Mbps. I urgently need a solution. I could barely access speedtest.net, and Google won't even load. I can't do anything. I am filing a complaint!