Use this link to determine if you have duplicate accounts with the same payment details.
On your current account be safe and put a payment PIN on it, that way nothing can be started without your say so.
If you did a search on the forum there are beyond endless threads with ways to get in touch with NOW staff.
Jump onto live chat and speak with staff. Make sure to click “chat online” within the green box, don’t hit “get help quicker” as this is a bot.
Or email support using the address in the below picture.
If you do have a duplicate account, use this email to get that account closed.
FYI that I do not work for NOW, just a NOW customer trying to help