Mortgage broker negligence? ?

My bank solicited me last summer to re finance my home loan. I agreed to apply. I was approved on a rate of 4.375 on 10-20-2010. I was told my credit score was 820. I heard nothing from the mortgage broker assigned to me for weeks. I emailed and called and eventually was told everything was fine and it took time. More weeks went by and I again emailed and called and the broker called me and said he no longer worked for the bank. I was put in touch with another broker. The new broker told me the loan had lapsed. He said he would try to fix it. Weeks went by so I contacted his supervisor. Supervisor has suggested it was my fault for letting the loan lapse and the loan rate was history. I said it was my understanding it was the mortgage broker's job to protect the loan not the client. I am looking for help as to my next step. Please help. I left out many details harmful to the bank such as many non returned emails and calls early on and later and that it took calling the escrow agent calling the bank for me to get responses. Please help! Thank you.