HELP! Former customer wanting to clear outstanding balance

Hi

I am a former virgin mobile and virgin media customer.

There is an outstanding balance showing on my credit file as a missed payment. Not a clue why or whether it is mobile or media? All equipment was returned and bills paid.

Customer service can not help as they can't gain access to the account - I don't remember passwords etc as it was in 2021!

This is extremely frustrating as I will pay any money which is owed and it's having a negative impact on my score but nobody seems to know how I can pay it.

Any help is greatly appreciated.

Thank you.