Changed phone number .

Hi there , could you tell me please what number i ring to tell Universal credit I have a new phone number as of today ?
( had to change providers as they were going to stop doing landlines ) I wanted to keep my old number but they said they tried but couldn't.
I have not received my first Universal credit payment yet ( should be 19th December).
I had help over phone from the Universal credit helpline, then a three way phone call over phone with DWP adviser and helpline .
I was migrated over from legacy esa . Many thanks M. W