Finding new ISP for elderly parents

[SpikyHatePotato]

My DParents have been having trouble with their ISP since August, new router(s) sent, succession of BT engineers - nada. Thank heavens for kind neighbours letting them use the WiFi.
I'm starting to look to see which company to change to - does anyone have any recommendations, please?
They only need broadband, no TV or mobile, and they want to keep their BT landline on the same number. They don't stream TV or play games, but do use zoom from time to time. It's mostly ordering click and collect, renewing library books and booking medical appointments.
It'll be a faff to change their email address, but the lack of service is now beyond a joke!

If they need to change their email address you could set up a hotmail, yahoo or gmail address. That can be used with any ISP.

They don't want to change their email address, but as the current one is ISP- specific, they will have to eventually. I'll sort that when we've figured out which ISP to change to.

<Bump> Anyone?

Zen is a Which? recommended supplier. and you can get to speak to their techie people without trouble.

Are they on fibre yet?
Which ISP do they have at the moment?

I had some teething problems switching to full fibre with BT, but since then it's been trouble-free. Traditional landlines are being phased out over the next couple of years and everything is moving to fibre and Digital Voice.