loss of voice mails

I work for a CPA Office, and we talked with a salesman in early October about lowering our bill and he suggested that we go to digital phone lines. We had the copper land lines. He told us that nothing would change that we could keep our phone numbers, fax number and call forwarding. We were excited. We never thought to ask about the voice mail and the salesman never brought it to our attention either.  So, the day came, and they had severe trouble getting us set up with the digital lines after two days of back and forth it was finally all working so the CPA went to check his voice mails from clients and there were none. The new ones gone all of the old, saved ones gone too.  So, I get on the phone and get transferred around 3 times until they get me to the right dept. just to be told that during the transition the old mailbox is deleted and that they do not have them backed up or stored anywhere. Now I know darn well that the phone companies back up and store everything.  So now as a business we have lost important messages from clients. The customer support person told me that this happens a lot and there is nothing they can do about it. Well first of all you need to train your salespeople to be informative and know the product they are pitching. The CPA has been an ATT customer for as long as he has been in business which is over 50 years. He may not be one for much longer if we cannot get to the right person to help us retrieve these messages. Also, when i called to try to get this fixed, I eventually asked to speak to the customer service persons supervisor, and I was on hold for over 45 minutes. and i finally hung up the supervisor never came to the phone.