Disconnects

Normally when they disconnect they have 5 minutes to come back. The tactic you name is one I have also seen. Yes it is a low tactic but, you should hear a sound when they eventually move. If you don't have the time to wait (and yes on the few moments I had this happen to me I was also irritated) don't start a game with longer time. But, mostly the people here don't use such tactics. You can always report the user to the staff, no need to get upset at chess.com for the wrongdoings of one person.

I have had something similar. The opponent runs out of time, reconnects and all your time is suddenly gone and he has all his time back.

That's because it isn't your opponent that's getting disconnected (or perhaps lagged), it's you! You don't see your opponent's move because you aren't getting information from the server in a timely manner. Your opponent's time continues counting down because your computer hasn't gotten the information from the server about your opponent's move or what their time should actually be. When the information finally does reach your computer, you find that your time has been reduced because all that time, it was really your move and not your opponent's.
This has nothing at all to do with what your opponent is doing, and they certainly aren't cheating.
Once more I have encountered a problem which I think many people here will recognise. I'm doing well, I'm a pawn up and my opponent, one , has a terrible position, he has a forced move to make but the "loading" sign came up 20 mins ago and there is no sign of life on chat. The last time this happened t danielschool registered a win I lost 11 points and he gained 150.
I complained to Chess.support. They said it was all perfectly normal!
They use the most complicated rating system there is: the "Blicko" and say that under that system it is quite usual for for someone with only one win in the last 10 games to see his score jump up from 602 to 1185 with just 2 wins (including the game I had with him.)
clock has now reached zero, mine stands at 27:20 He will now reconnect, make a move which I will not even see, and be credited with a win and if I dare to complain about it to chess.com/support all I'll get will be a load of bloody cheek.
The screen is now frozen and I cannot have another game unless I uninstall and download again. That's what I've just done and I expected he has registered another move which I didn't even see and I have lost 8 points he has gained 11, even though he had a higher rating than me.
Could someone explain to me how they are able to do this and what's the best thing to do when it happens?
To Chess.support: don't bother me again with your pathetic excuses. There's a simple solution, besides giving me my money back and that is to bar these pathetic cheats.
You would think that you would value my custom more than them because I was foolish enough to take out a subscription, but I suppose your real money comes from advertising and you're desperate to keep the numbers up.