Capped FLTE problems

I switched to Supersonic in the hope of better internet speeds in my area. Initially it was great. Received a router in time, had minimal issues setting it up and got an average of 25mbps internet speeds. About a month ago, it started to go in the wrong direction. I am lucky if I hit 1mbps. I have been told multiple times to “move the router, switch it off and on, reset it, connect it via LAN instead of WiFi, use other devices to check”. Even had the simcard checked and having Supersonic check the cellphone towers in the area. No joy. Then the next fantastic thing hit us…we have a capped 100Gb line, and had 29Gb rolled over from the previous month, but according to my account, I used 139Gb, essentially 10Gb into the minus (how this is possible with a capped subscription is a mystery). Topped up the account with 25Gb, but within three days, my internet is disconnected again. Checked my balance, and suddenly I am at 154Gb usage, my rolled over data is not there anymore and it shows I am 29Gb into the red. Foolishly loaded another 25Gb (at R150) to still be 4Gb in the red. Now as I was reading the reviews tonight, I came across one that indicated a similar problem, and that there is a system glitch. How a capped account can go over the allocated data is a mystery, and with exceptionally slow internet speed, manage to rack up so much data in such a short time. I switched to normal mobile data just to get some work done. Still waiting for an answer on the slow internet, and now this hell. Seriously considering canceling my subscription and moving on