First thing I would do is to pop outside and see if the installer has taken the easy way and ‘spliced’ your neighbour’s connection into yours. Look for the (usually) brown omnibox on the front outside wall and just check if a ‘new’ cable has appeared leading next door!
Your power levels are quite low, technically still within spec although if we have a hot summer, I fully expect your connection to collapse completely. I’m more concerned about the lowish S/N ratio on a number of channels and hence the large number of errors being reported.
One other possibility is that the installer for next door, having some trouble getting it working, ‘moved’ your connection in the street cabinet in favour of your neighbour’s and connected you to a bad, or unsuitable tap in the cabinet. They shouldn’t do this and they certainly wouldn’t check with you afterwards to see if your connection was OK. I can sort of see their incentive, get the job done, they get paid, only a small risk of messing up someone else’s connection, even if they notice, but either way this is now ‘someone else’s problem’, and not theirs!
You’ll need a tech visit to fix this.
