First Utility renamed Shell Energy – here's what you need to know - MSE News

JEO wrote: »

Foolishly, I switch to Shell Energy only to find in the absence of any bills that a) their servers cannot read my Econ 7 smart meter or b) by first generation gas meter - important facts not disclosed in the personal tarriff information they sent me after the cooling off period.

Anyone with existing smart meters probably already knows, or soon discovers after switching energy supplier as you did, that their smart meter then goes dumb.
It doesn't usually matter who you switch to.
The recent introduction of SMETS2 should mean this is no longer an issue, but the majority of those who have SMETS1 will have to await an OTA update.
You can read more about smart meters here:
https://www.moneysavingexpert.com/utilities/smart-meters/

JEO wrote: »

Trying to contact them is also a very time consuming and frustrating experience: 20 minutes to obtain a reply on my first call; over 40 minutes in a second call. Email is little better. Days before receiving a reply that did not address all my questions.

You can read more feedback on Shell Energy (previously known as First Utility) in the feedback thread here:
https://forums.moneysavingexpert.com/discussion/4415653/add-your-feedback-on-energy-supplier-shell-energy-formerly-first-utility

JEO wrote: »

And still no bill after 6 weeks into my contract despite submitting meter readings.

Shell Energy usuallly bill according to traditional timescales. i.e every 3 months, as stated in term 4.2 I believe of their thems and conditions, which presumably you were provided with and accepted when you switched.