Switching.

Hiya
I’ve switched to bulb as of today, but I’m not sure how bulb will be supplying my electric, I’m on a smart meter, top up as I need too, credit is very low, which will go into the emergency, which will then mean I need to top up but I’m also paying monthly, so not sure what will happen once the money does run out? Will my electric just cut off? Will I still have to up with the old company?