Unsellable house. Damaged roof

We got our solar panels in 2012/2013. A lovely salesperson came and sold them to us that we would get lots of electricity/ increase value to the house/ all the bulling it up. We signed up understanding we were in a 25 year lease but we weren't concerned as we were assured that it would add value to our home and were backed by the government. 10 years on, we are left with a house we can't sell, extensive damage to the garden, guttering and roof caused by pigeons. We have had to rent the house out which we didn't want to and even though we have had several conversations telling them we don't live there and to contact us at our new address so we can liaise with tenants for servicing (which only happens if they get a problem) they still consistently send mail addressed to me to the old house. The tenants don't open it and instead once it gets to a pile I collect it. We have been fined for not being in at an appointment that we didn't arrange. We refused to pay it. We have now spent 1100 soon to be 1500 to get mesh around the panels that the birds keep getting under. Beautiful garden is ruined with all the rubbish the birds drop and random seeds. It's a constant source of stress. I need to sell the house because it's no longer financially viable to keep it with the way the interest rates are going but I can't. We even tried to sell it to a we buy any home type affair. After getting it valued by them for 70k which was under the average value but we were willing to take the cut to get rid, they came back after all the paperwork had been done and said the contract was very dodgy and would be problematic to sell on as a result. They wouldn't lower their offer because at that point I would have took lower just to get rid of this constant source of stress and said it's basically unsellable and no solicitor will pass it due to the contract. We don't have a signed by them copy of the contract. Our contract wasn't witnessed and there's several clauses in them which are the issue. I would never recommend anyone deal with this company. A shade greener are an absolute fecal matter show !