Possible scam help

My elderly dad has been receiving calls for a week from Virgin Media urging him to renew his contract. 

He answered today and was on the phone for an hour. He is happy with the offer but I’m concerned as they asked for the first 5 digits of his bank account and his date of birth. 

is this something virgin ask for?

He has got an email from them but haven’t been able to see that yet to check it looks real. 

Thank you