How long does a credit card company have to collect before it is taken off your credit?

I declared bankruptcy in september of last year. Before I declared I got a credit report for all three of the credit agencies to make sure i didnt leave anything off the report. I had previously had a discover card from 2000(that went to collections) but it wasnt listed on the account, so i didnt put that on the paperwork. Im not saying that was the smartest thing, but that isnt my question. I recieved a call from a lawyer today stating that I owed it and if i didnt make arrangements to pay it by the end of next week I was going to get it taken out of my check. I just looked at my credit report again(all three of them) and it wasnt on any of them. I know judgements and items that go to a lawyer are listed on there, so can discover still collect if it isnt on any of them? And after 7 years, isnt it taken off of your credit? Again, it is from the year 2000. I put a call into my bankruptcy lawyer but I wont recieve a call until after the holiday weekend.