Refund of my deposit from Petchey Holdings commercial unit landlord

[Trugmakers]

According to the terms of my lease, I have left the commercial property in excellent state of improvement. Although the landlord (Large company) has no problems in this respect of this and is advertising the Unit for re-leasing. They have not returned my deposit of £4,000. The lease states it will be returned after one month, but it has now been 7 months. My emails are mostly ignored, I have 2 emails stating that the release of deposit has been authorized, but still not. I have sent a 'letter of action' that expires on 7th May but I am certain this will be ignored. Is my only course of action from the 7th is to proceed with the action?

[atticus]

It would seem so.