Exactly what I thought and exactly the same problem with my electric. Moved from EDF . Readings started ok then stopped on the app May 13 th then.... nothing .
I've contacted them and they say they have forwarded it to a dept to get back to me but it is worrying about going from credit to debit .
"Thanks for taking the time to get in touch with us about your billing complaint. We're sorry that we've fallen short on this occasion.
There seems to be an issue with us receiving meter reads from your electric meter. It worked for a few days, and then stopped. I don't know why this has happened, but I've flagged the issue with smart team under a complaint to get the reporting issues resolved.
I'll try to resolve the issues with your bill in the meantime, but it may be that we're unable to generate a bill because we haven't received meter reads from your electric meter (thus don't know what to bill you).
This might take a few weeks unfortunately."