Modem Storage Overload?

I'm having this same issue as well as extreme buffering. The device has went from 4 down to 2 bars in the last 24 hours & I cannot even connect to the internet on my television or even on T mobile phone via Wi-Fi. I've been patient since receiving the 5G gateway in March '21, but I'm ready to quit. I've rebooted, unplugged & reset so many times I forget how many. They sent me a 'new' replacement that had a small notice of being refurbished inside, but it was simply someone else's  used device & I returned it. T mobile has tried to correct the issue, but it seems they just don't have the know how.