Who was your provider, and who is your new provider?
I was having both bad connectivity to Spectrum as well as buffer bloat, which I think was upstream. Had to get Spectrum in three times, after which the spent several days up on the pole and in the field doing major work, and the problem resolved.
This was in Germany, using Vodafone (Kabel Deutschland), moved to "supervectoring" DSL and life was better (it's not fiber, but it's second best) - wrote it up at the time here: https://arahayrabedian.github.io/cable-to-dsl/
My neighbors still have problems with the cable connection.
I was having both bad connectivity to Spectrum as well as buffer bloat, which I think was upstream. Had to get Spectrum in three times, after which the spent several days up on the pole and in the field doing major work, and the problem resolved.