How to get your apartment mail box or cluster box lock changed?

We lost the master key to our apartment cluster box (mail box) located in our building. The landlord told us to go to the post office and have them change out the locks. We then went to the post office and we were not even on their list for mail delivery. We went back to our manager/ landlord and they said they would ask the mail lady. The mail lady could not provide any information on what to do. I called USPS and they said that the mail box/ cluster box could be owned by the management Company. The management company we have is I.C.G. "You're in Good Company" Residential Management, but I cannot even find a number for them. We live in Fountain Lakes Apartments (Used to be called Versailles on the Lakes) in Fort Wayne. Its seriously become a problem and we have no idea where to go from here. The ladies in the office are really nice, but they should be figuring this all out for us. Its an old mailbox anyway and we had problems with getting the key to work half the time anyway. Does anyone have a clue on what we could do? Thanks if you can help! ;)