German help!

So I'm currently living in Germany and studying German. In the Umgangsprache it's very common to use the dative when you say "wegen," so much so that I thought it was the rule, but my German teacher told us that "wegen" is actually supposed to be used with the genitive. I was wondering if anyone could tell me if in older German there were personal pronouns that could be used in the genitive case?