Slow Speed-paying for 1.2gbps and getting 25mbps

I am not sure who to contact at this point to get it corrected because it seems like no one can figure out the issue. It started over 6 months ago when we received notification we would have service disruption due to work being done in our area to prepare for an upgrade. We started to experience slow internet connection shortly after. It was slower but still manageable. Over the past 6 weeks it has become horrible. Our internet is getting anywhere between 25-50 m when we are paying for over 1000. This is causing our wireless TV boxes to freeze and pause while we are trying to watch TV or stream. It has gotten so bad now that it happens every few minutes. My children are also having issues playing video games.  I used the app several times to trouble shoot and was eventually prompted to schedule a technician. The technician came out and looked over a few things and determined we needed a new gateway. This seemed to work for a few days but the issue started again. I used the app again and a new technician appointment was scheduled. He spent more time trying a few things and eventually determined the line underground that was feeding the internet from the box to our home needed to be replaced. This took almost 2 weeks but we were hopeful this would correct the issue. The line was replaced and it helped for about a week but we started experiencing the issues again last week. A new technician came out this past Saturday and spent a good amount of time working on things outside but could not figure out the problem. Our service is now worse then it was before he came out on Saturday. I am extremely frustrated at this point. Any advice from someone who has had the same issue and has gotten it corrected would be helpful.