You need to do some investigation in your own. See if your neighbors know where the cables for phone/cable etc go into the units and where they come from. Once you’ve tracked that down look inside and see if you can find where they come in. The cable outside to your unit should be fine even if they remodel ruined what’s inside. From there they should be able to come inside and find where the cables go. As you said they may have tried this already. Worst case someone needs to cut a small hole in the wall where it comes in. Depending on where this is you could just have a jack and out the network equipment close to it.
At this point the suggestion to get a low voltage electrician might be your best bet. You will pay more but they will do a much better job than the cable installer. Have them run coax/cat6 where ever you want things to be.
Interesting it’s loaded. Maybe I’ll swap for u loaded, I have a ton of keystones around