Hi, Janice! I did a search for the "communi" of the "Provincia di Foggia", and there is a town called Monte Sant'Angelo, which (if my limited Italian serves me) is the center of the highest elevation in Gargano.

I checked out the following website:
Comuni-Italiani.it
and looked at the provinces of the Puglia (Apulia) region. None of them (Bari, Brindisi, Lecce or Taranto) with the exception of Foggia, had a city similar in name to what you described as "S. Angelo di Bsig."

If your relative was from "near Roseto Valfortore", chances are that the town he's from is in the Region of Puglia, province of Foggia.

You can also check a map of the regions of Italy to investigate nearby regions to Puglia, their respective provinces, and those provinces' cities.

Hope the above information helps!