Poorly managed property

My agent has managed the property for last 5 yrs. the tenant stopped paying and left the property leaving it a mess. The agent put together a list of things that should be sorted and told me they were pursuing the tenant through judges demand and they would pursue the guarantor too. The list they sent to me was for £4500. It turns out after me pursuing them for progress that there is no guarantor agreement despite them telling me there was. I have asked for copies of all the documentation several times but have received nothing from them. Shortly before all this happened there was a report on the condition of the property showing lots of mould on the walls. I asked them to sort this and was charged £200 for it. When I got the property back 3 months later the mould was in the rooms and covered the walls and could not see how they could have treated it. The tenant had clearly had a dog that was never agreed with me and whilst the agent knew this they never did anything about it.

I have no idea what to do next but am furious that they can perform so badly and get away with it....can anyone advise?