I just did about an hour and a half of cleaning and packing in the kitchen, and already need a break...
Um, I'm like that & I don't even have MS.

My IAs...I'm cold, which means I need/have to get out of my bathrobe & get some clothes on, and I'm hungry - so I need to walk downtown here & get something for lunch because we don't have much ready (like now!) here. But I also want a nap. Am pondering putting the heat on...

You can't change suppliers if your present suppliers won't release you and they won't release you if you are in debt to them.
If you don't respond to their letters granting them access to read the metre and don't pay them anything by standing order or by crediting their account, then they can install a coin operated gas metre in the house. This means they set the rate at which the debt is settled, for each coin you insert. Landlords don't like metres in houses because it puts the next tenant off.
The best thing to do now is to grant them access to read the metre, then get talking to them about a repayment plan and keep to it.
It
may affect ability to switch suppliers, but it's not an impossible thing. They have the right to object to the switch, but in practice, they don't universally do that. No one is saying 'don't pay the bill'. I speak to people
all the time, who have switched energy suppliers, and are slowly paying off the balance on a bill for the previous supplier at the same address. It's not uncommon. It
might mean having a key/card metre installed though, which isn't the most economical way, of course. And as my post reads, if
worst comes to worst...