Internet keeps dropping even after new line added

A few months ago, I stopped into an Xfinity store to renew my contract. They boosted my speed and claimed I needed to replace my modem/router combo. I took home the new router and swapped it with the old one. I returned the old router to the store, and my Internet has been dropping ever since intermittently.
Somehow, I got a service tech to come out and they claimed they squirrels had chewed through the line. They added a new line. (The old line is still out there even though the tech stated they’d remove the old one soon).

My Internet connection still drops at least once a week.

It’s quite frustrating, as I’m paying more for a faster connection and the connection drops so often.