Best answer by Jon1
Hi and welcome.
Your old supplier did not update the national database when they installed the new meters. This is why everyone insists on using the wrong figures.
Once your switch is complete then PP can sort it out and get the details updated to the correct info. It will take a few weeks to do but it can be sorted.
Your only other option is to cancel the switch and get the old supplier to sort it out, but it seems you tried that already.
Only your current supplier can alter the database.