I am in the same boat. Just moving over from British Gas and have taken my readings from my smart meters and enter them and it comes up with an error message. Tried to do an online chat without success..
I read from someone else suggesting taking photos of your meter readings with serial number showing as proof which I have done..
I have just switched from SSE and have been trying to send upto date readings of both gas and electricity. The gas has been confirmed and I've paid outstanding balance to SSE, however trying to confirm electricity has been a nightmare. Tried submitting on the App, through the login and the automated call number. All Iget is an error occurred ! I've been in contact with a really helpful guy from SP who has submitted the readings again, now just waiting for confirmation .
I have sent letters I have sent e mails I have phoned all to no avail no one answers I can't read meters need firm to do read the meters no luck been asking since January so dissapointed with Scottish power need to change. They don't look after the customers loyal customer does not count.