Channel stuck open on call forward to cell

Phone system has worked great for years. Client has a virtual image of FreePBX running on a Windows 7 desktop. Client wanted to try out call forwarding to cellphone. Phone call will come in to the front desk who answers it and they need to speak to the owner they forward the call to the owner's extension Grandstream phone IF he doesn't answer after a few rings FOLLOW ME then calls his cellphone. Owner then can answer his cellphone. Here is where the problem randomly happens. The conversation is made between the owner and caller and they hang up BUT the call never ends in FreePBX. A channel seems stuck open and never ends. This builds up after a few calls and all channels will be congested after some time.