Help with letting agent and contractor issues

Letting Agents

I have a rather juicey case to discuss. I had been renting an upstairs flat where the downstairs flat had owner occupiers. We had had an ongoing issue with a leak from the upstairs flat with numerous complaits from downstairs. Attempting to be the most dilligent LL I could be, every time I received a complait I contacted the letting agent to investigate and set remedial works. Now, in the summer of 2023 I spent around £700 on repairing this leak, these contractors were sourced by the letting agent I had been using and I was assured that they were the best of the best and that it would involve a 12 month guarantee. I should also point out that I have been a fairly hands off landlord with this property and the letting agent had been in full management. I had another call from downstairs in the autumn saying that the leak was still there so i contacted the letting agent who said that the tenant had advised that in fact there was an issue with a gap in the window next to the shower that was causing the leak, obviously this was not picked up by the contractors in the summer, somehow? The tenant, who was due to move out, said that they had taken measures to rectify the issue for the meantime until I could gain access fully. The tenant ended up staying much longer than expected and I had another call from downstairs about the leak so I called the letting agent, in fairness it was not the usual memeber of staff I spoke to as they were away, but I felt like I was met with a relatively dismissive reponse about downstairs flats always getting leaks from upstairs and not to worry, I foolishly took this advice. The tenants have finally left the property and that same say I have received pictures from downstairs showing me that half of their ceiling has now collapsed due to this leak, thankfully their flat is empty so nobody was hurt. I have agreed to pay the insurance excess for the repairs to their property but I am feeling that a lot of this has been caused by sloppy tradespeople as well as management that does not really meet the cut. I would like to know what the concensus would be as to anything I could do in regards to reclaiming some of the costs from the contractors? Or indeed what ideas people may have about this case in general? Any advice would be appreciated, thanks in advance!