Need advice ASAP

So I have detailed billing in our phones ! We share a line. So anyways the bill information came today and I read it and saw a number my boyfriend likes to text between 3:30 am - around the time he gets off the next damn day which is 3:30am. This number is consistent and isn’t any family or friend I’ve already checked ! What should I do ? Apart of me says wait for next months to see if I see the same pattern and then other part says ask him about it now ! He doesn’t believe the phone company would really send a bill listing every call and text that was made and received including times and duration of phone calls 🙄🤦🏾‍♀️

UPDATE :: I took y’all advice and text the number ! Y’all I feel so slow lmao it was his GRANDMA literally his grandma ! She called my phone once I began texting 😂😂😂😂 I feel so bad lmao