I had a similar (not identical) experience when a solicitor I was using ran into difficulties. The replacement solicitor was able to complete all the outstanding work at no additional cost to me as I had paid my final bill and was able to prove this (cheque stubs, bank statements, etc.) It took a few weeks to sort but the outcome was OK. If you have paid, you won't be asked to pay again. Check the letter you got from the Law Society, it should (as best I can recollect) mention not paying again.