Rotten deck not replaced as promised by just letti

We looked at the house en of February 2016 and the wooden deck was rotten, she said the owner is going to replace it and we can move in the 29 March, when we got to the house the deck was not done my wife went to them on the 30th to report, eversince we try to get help I send e-mails phone her boss nothing. On thursday my wife nearly got hurt when walking one of the planks broke. We send a mail with photos, she then said they are coming on monday to give a quote. I need to cansel this contract and look for another house , but now they say I am going to loose my deposito, which is unfair because they did not do what they promised, if I knew the wooden deck is going to be a problem I would have not taken the house. At this stage we risk every time we walk on it and it is the only place you can walk. Even after I spoke to the manager I was not helped