Feedback appreciated!

In Nov 2023 we bought a house. The seller had a mortgage with Santander. We bought with out a mortgage. Bank representative was not present at the notary. Purchase tax has been paid and all other associated costs. Solicitor (well known and respected) keeps chasing Santander to remove charges via "certificate" from the deeds. In April the seller came to the bank to sign a document back dated to November 2023 saying the mortgage has been settled (paid off in full). Santande