Inform them that you expect the settlement figure based on the date you applied to surrender the policy, if there is a shortfall due to their delaying tactics and they refuse to "make that loss good," caused by their inefficiency then tell them you are going to complain about their unfair treatment and request the return of your lost money to the FOS, be fully prepared carry out your promise if they still refuse.
http://www.financial-ombudsman.org.uk/