Just finished mission Misappropriation, killed fbi agent and got the file, said mission was complete but nothing has happerned since, have no missions for other people and no new symbols have come up
Any ideas?

Do a search for San Andreas Walkthrough and you should be able to get your answer.

I think you need to wait for a cell phone call or you need to go to the garage or something as I recall

Maybe you stumbled on a bug. Try reloading an auto save or a previous save, go through that point again and see what happens.

Also try applying the latest patch. It might fix the problem.