Cell phone delay using att microcell

For the past few months I have no problem making cell phone calls and both sides of conversation are audibly good. However, when I receive a cell phone call it takes anywhere from 12-20 seconds for me to be able to hear the caller's voice wihout it breaking up. The caller can hear my voice perfect from the beginning of the call. I have a Netgear 3000dv2 Modem which is not dual band., but is what Cox recommended last year. I have an ATT microcell tower that plugs into the computer and is like a mini cell tower in home. ATT has told me that they have a cell tower about a mile from our home, but the reason we obtained the microcell tower was that the other tower must have turned their power down and our calls started dropping regularly. I did contact Netgear Support and they checked my computer remotely and indicated that Cox only supports up to 15 wifi devices and can not handle more than that which affected my microcell tower and the calls. Any solutions? Do I need a dualband modem router?