this one is hard. all i could find is the French Patois (dialect) word Vonchelle, meaning 'bindweed, convolvulus' (a plant). This happens often, that a plant is used as a firstname and this plant is a herb, like
Basil and
Sage. But if this is the root of Voncele, Voncelle, Vonshelle, Vonzelle and all the other variants, i'm not sure. I found even little evidence that it was from French, it is either hardly used there (today and in the past) or not from
France. Vonzelle at Google.com came back with some
German sites, though, but mostly American sites.