Rent increased but work not done!

[Courtjester]

I currently rent a property through a letting agent acting on behalf of the landlord. I've recently received a letter from the letting agent asking me to increase my rent, and included a form signed by her (the letting agent) in place of the landlord (it just so happens that I don't trust this particular letting agent). Should it not be signed by the landlord? Also, there are some problems with the property that have not been resolved; My balcony door was broken last year (the window smashed and the door split) because the wood of the door was rotten. I have told the letting agent several times yet still nothing has been done and for the past year I've had bubblewrap keeping out the elements. Also, I had to have my toilet cistern replaced, and for about 18 months I have had to put up with a cheap plastic version that doesn't match the rest of the suite and needs to be flushed twice before it actually works properly. Is there anything I can do to get this work done? Can I refuse to increase my rent until the work is done?