Best answer by Mavis1
You would need to contact the team via help and wattbot. Type message the team and then explain the situation.
Or you could if still in the cooling off period cancel the switch and start again in 3/4 days time once the cancellation is done.
Or just leave it as it is after all i presume your mum can be trusted to pay the bill. Plenty of others have accts like that, me included.