AT&T TL96457 Bluetooth phone system not working with bluetooth

I have my second AT&T TL96457 Bluetooth phone system and it eventually did the same thing that the previous one did. Initially, I was able to pair both mine and my wife's Android cellphones to the base system, via Bluetooth and it worked fine. After a few months, it is like one of the phones gets stuck in the Bluetooth mode and you can't disconnect or delete it from the base unit. I have tried unplugging it for an hour and plugging it back in but the same phone shows Bluetooth busy when trying to do anything with it. Very frustrating. The original one was replaced and now the second one is doing the same thing. No one seems to know how to reset the base unit to factory and start over. Can anyone help me please!