Do you really want to hang around with people who take the piss because of where you come from? Stick with the people who appreciate you for who you are, not who others think you should be.
I've had a similar experience. I'm not sure whether I'd class myself as working or middle class (I'm not really bothered so I don't think about it that often!) but I come from Lincolnshire and people seem to have a problem with that because it's north (apparently - last time I checked it was in the Midlands, but anyway!). A couple of days ago a girl said to me "do you say 'bath' and 'grass' in the posh way or the chavvy way?"... And when I told her I said "baath" she looked surprised. I asked her why and she said "well, you're from Lincolnshire." Eh yes, have you got a problem with that? (I wasn't even aware using short vowels is chavvy but there we are!).
So I don't think it's uncommon to be judged on where you come from but at the same time, I don't think it's particularly acceptable for people to judge you on something so superficial either.