How do I get my Housing ociation to buy my share of the property?

I bought a 60% share in a local housing ociation property in Blackley, Manchester, seven years ago. Since then, due to the cosntruction company laying the wrong pipes, my house has flooded three times - leaving me homeless each time. I'm desperate to sell because I can no longer meet my mortgage payments, but am having trouble. The ociation have finally admitted liability for not properly overseeing the building work and are going to put it right. This involves major work through my garden involving the siting of a holding tank and control box for a pumping station to deal with the drainage problems. Does anyone know of a way I can pressure the ociation into purchasing my 60% share? They know I cannot pay my rent to them, or my mortgage, because of an unexpected illness and that selling is going to be very difficult. If anybody can help me with this problem, I would be most grateful. Many, many thanks in advance.