The usual response on here to this is that VM can't/won't (maybe because they can't readily access the info?) tell you what the charges were for in the sub-50p category.
Suggestions on here for possible explanations often include things like an occasional call over-running the 60 min call limit and generating a charge or sometimes equipment such as call blockers unexpectedly dialling out, outside of free time periods (which actually happened to me recently, although I recognised what it was)
AFAIK you can only get the info via a DSAR
https://www.virginmedia.com/help/dsar
and requesting your call records.
VM's speed at providing these DSAR requests is often mentioned on here as being rather slow, so if it is just a one-off small charge you might want to balance that against any unhappy admin effort of having to communicate with VM
You could also request VM implement full itemisation on your phone bill. That way, if anything chargeable crops up in the future, you should be able to see what it is and the number involved.
