How do I actually get a hold of a xfinity tech?

Comcast tech was working on box in yard earlier in the week. Now my internet drops out occasionally and is slow. I am only getting 100Mbps of the 300Mbps that I am supposed to get. I do realize that cable internet is shared with others in the neighborhood. I have never had a problem until the tech did something. I would like to know a few things:

1) What did they do exactly? It appears they installed a new concentrator that services the neighborhood. If they did, do I need to upgrade my modem? (It is a Arris SB6141, DOCIIS 3.0, so a little on the older side).

2) Can they fix my line? My downstream power level is 13dBmV, which is a little high (outside of the -10dBmV to +10dBmV range). Can they just throw a 6db attenuator on there?

3) How do you actually get a hold of a real person? I can't, for the life of me figure out how to get someone on the line.

I have tried the useless virtual assistant on their website. Garbage. I have ran through that 20 times, changing my answers every time, just to see what happens. Same outcome. It always says that it is something on my end.