Do I believe it ?

LONG STORY! Ok so a few weeks ago I had a text of some girl who my boyfriend has slept with before me 😷 saying 'slag' my boyfriend was like ring her she's trouble causing . So I did she then said ask your bf when he was last up mine ! So he rang her while I was there and she kept on hanging up the phone ... I text her saying if this is true tell me when .... she said she didn't know ? My boyfriend wants to go to her house to ask her what she is on about . She's now blocked me off everything . Do I believe her ? I don't think my bf would make me ring her if he has anything to hide plus he's never missed a night at home he's always come home after a night out even if it has been late ?