When does Deed in Lieu become official?

[Mike]

After a several month process our lender (Countrywide) agreed to a deed in lieu on our property. The negotiator told us it was approved, and we received a warranty deed in the mail from a company called Trustee Corps. We signed and notarized the warranty deed, returned it as instructed and moved out of the house. Now (almost a month later) we receive a letter from our lender saying they canceled the deed in lieu. I called them and they are claiming they never got the paperwork back (and never bothered to check in with us about the status before canceling). This is very frustrating after all we went through to get this approved and following through on our end. I don't know what happened with their copies of the paperwork - I definitely mailed them - but I have a copy of the Warranty Deed saying we are released from all liability on the property and that the property is granted to them. Will this hold up legally? I do not want to go through the whole process again! We were so excited to move on with our life and now this happens. Any advice would be much appreciated.