Hub 3 replacement

Hello all.

I have had a hub 3 for the last 5 or 6 years. Recently it has started to play up. The light on the front stays permanently red. This has been an issue for a number of years. Back then, when I reported it, an engineer called.
He tested it and it told me it was fine, "Probably a software glitch" he said.
Since then I have moved home. Now with the grand children visiting. They have all grown up now. And all have iPad's etc. 
I have now noticed the hub will randomly disconnect TVs, ring door bells, Pcs Etc.
I suspect the hub is being over loaded with all the extra traffic. I have upgraded to the M 250  5 days ago.
Unfortunately this has not helped.
I have tried to call on a few occasions. Every time I have waited nearly 30 mins to talk to some one. Only to be connected with someone I cannot understand. It happens every time I call. I have asked to speak to different people, only to be faced with the same problem. I really have given up at this point.
Sorry I'm so frustrated.
Anyway. Question!
If I were to get my hands on a hub 5. Bought of a certain website. Could I connect it without any problems. Is it plug and play, a direct swap for mine?
I know this equipment is rented. However people do sell them. I don't want to cause any problems.
Unfortunately I cant see any other way. I'm now stuck with a new 24 month contract and a hub that's now no longer fit for purpose.
Please don't advice call customer services. I have given up on that!
Many Thanks