The OP said that he made test calls from a land line at his office. You can usually tell a crappy cell phone call.

I think the problem is that he is relying on what the customer is telling him and hasn't spent enough time at the site to check the problem out for himself. At this point there have to be calls that are directly answered with the problem. Do they even answer any calls or do they have the AA do the transfers? If the former then you have to go put the AA on a delay and instruct the customer to answer calls directly (or you stick around while making test calls until you can duplicate the problem).

I suspect that this is a service provider problem since this is the only thing left. Possibly related to only a one or a few lines but without proper testing this is only a guess and you are going to need all the ammunition you can get to get them to even talk to you.

-Hal

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