World's worst landlord

For the last 7 weeks Tim and I have been hounding our estate agents to come and fix the problems in the flat. I'm unsure how long things have been breaking as I have worked 6 days a week since March so haven't spent much time at home.

Today was the final straw as I notice a mouldy window in our bedroom. A blunt email to the agents which said I will not be paying another penny rent until this is all sorted should have done the trick. But it didn't. They just said their handy man was 'caught on another job'

A leaking boiler, 2 windows that don't fit and have a gap of 0.35 inches along the top, a hole in the roof, 3 mouldy windows and a front door that doesn't close properly.

Am I wrong to not pay any rent until this is sorted?!