You are right, V and B are pretty much the same, in fact in Hebrew there is only one character for both (
Beth). It is only one little dot that makes the difference between the two and for a long time none of these dots and little lines were written in Hebrew. As far as I know the Greeks got their alphabet from the Phoenetians (is this how you you spell it?), and their alphabet was rather close to the Hebrew one.
When the bible was translated first into Greek and later into Latin, all Beths were turned into Bs, no matter what the Hebrew pronunciation was at the time. So in the Hebrew bible you'll find
Avram and Dvora and some people nowadays return to this old spelling and pronunciation and may name their child Rivkah instead of
Rebecca.
But of course
Isabella is not a biblical name;
Elizabeth is from the Hebrew
Elisheba,
Elisheva resp.
So I would think the change in your name is due to someting else. I know in Spain they pronounce V and B the same, but I don't think they would change
Isabella to Isavella, as
Isabella is a typical Spanish name. So maybe it did happen in Greece after all, or maybe it was the idea of an individual …
If you find out more about your name, please let me know. Thanx!
Andy ;—)