Just moved house agency from old house being very rude and threatening advice needed?

I have just moved house. The house I moved from I had lived in and rented for 6 1/2 years. When we first looked at the house before moving in we thought the place was a joke. It was discusting. The carpets were badly ripped and soaked in dog urine and there was dog urine over the walls and the house was generally dirty and not really habitable.We walked away but in the end had to change our mind as we were desperate. We could not find any where else to rent and had a baby and needed a roof over our head. We asked the landlord if he could change the carpets and re decorate he refused. So before we could move in we had to replace all the carpets at our own expense and had to re decorate at our own expenss. We never like living there are all the time we were looking for some where else but could not find any where. The house was horrible. The hot water and heating did not work properly, the gas fire did not work and was the only heating down stairs. They never had the boiler or gas fire fully serviced in the whole time we lived there. The back of house kept flooding but land lord would not do any thing, the house had big damp, mould and mildew problems in every room. We are so glad to have finally left that house. When we moved out we completly redecorated and cleaned the house well. Today I recieved a very rude threatening letter demanding I pay for thing that were already broken when moved in, they say my decorating was not good enough and that ive got to pay for a proffessional decorator to re decorate whole house. The list goes on its rediculouse, they even state some thing about a new pair of trousers that I need to pay for as they aparently got covered in paint which isnt possible as when handed key in all paint was dry. What are my legal rights do i have to pay this huge long bill. Is seems rediculous and unfair and I feel the land lord and agent are having a laugh. It clearly states in lease agreement that have to leave property in same condition as when moved