I am not sure how you were able to sell the home and transfer title with the mortgage being satisfied. There is a mortgage lien on the property when its financed. Did you not use a real estate attny or title company for the sale transfer? That is what they do -- insure clear title.
If you are hoping to buy a house, you likely have a budget in mind. Hopefully, that budget includes fees that come with the process, not just the purchase price. The good news for buyers is that they aren't directly responsible for paying their agent. Agent fees usually fall on the seller.