Thank you again - I obviously haven't yet understood what "genitive" means - I thought it was to indicate possession, which I would have thought was always the case with twoj etc. I think I was asleep when they taught cases at school!
Mostly genitives are either possessives (words with 's on the end) or words with 'of' in front of them. Polish converts all negative direct objects into genitive, so in this example you can think of it meaning:
I have not of your address.