Problem with Old Letting Agent

We have recently changed letting agents as our old agent was not actively managing the property or collecting rent.

We have been trying for several weeks to get the letting company to send our files to our new agent who needs this information to change local housing allowance claims over and take over an eviction procedure.

Our old agent is not finding time to send the information and his staff advise us only the manager can authorise the transfer of details.

We have offered to drive to Hull (350 mile round trip) to collect the files but are still told unless the manager is in the office (which is rare) they will not release the files.

How can we obtain the information (which is surely ours by right) so we can get our properties effectively managed again.