Very poor internet

I subscribed for a Vox line and got it installed, because my wife got a job and working from home. The line I subscribed for is 20mbps download and 10 upload. We have been experiencing a lot of buffering in the house, the calls over internet that mybwife has to make were not so clear. On the 17 th November I called and logged a complaint about the quality of the internet we are getting told them the speed we are getting goes as low as 5mbps. They told us they fixed it on their side, the next day the problem persisted. I called again and reported it. Today my wife lost her job. Vox is not good at all, so unreliable service.