mkaye wrote:i called my cell again & hung up
I'm not clear on what you're describing. Did you cancel (hang up) the call before answering it on the the cell phone side?
If so this is what should happen:

(example 1)
FPL did not detect hangup
Based on the cellphone continuing to ring after cancelling the call on the FPL phone side?
When I call my cellphone from FPL and cancel the call before it's answered, my cellphone stops ringing. I tested using all three FPL proxy servers.
Or did the cellphone side answer the call and then hang up from the cellphone end of the call?

(example 2)
In this example, the callee (cellphone) is hanging up after answering the call.
not sure where to look
In example 2, BYE is presumably being sent back to FPL's proxy server, and it, should be, in turn, sent back to you.
So you can check SIP logs to see whether BYE is being received/processed.
You can also check to see whether 200 OK is being sent from you to FPL after BYE is received.
If you are not receiving BYE, I would eliminate my router from the equation, briefly, and test without it to see whether its NAT firewall or some setting is causing a problem.
I would also check my Contact headers. BYE is sent to the IP address and port listed in the INVITE's Contact header; FPL's servers attempting to send packets over the internet to private LAN IP addresses (ex. 192.168.1.28) can cause problems, for example.
My response is the same:
viewtopic.php?f=8&t=20678#p81154.
"BYE was not either not received or processed. I would suspect a problem with NAT association, although I have no idea what caused it for you.
Does eliminating the router resolve the issue? Was router firmware updated recently?
Again, I suggest asking at
https://community.freepbx.org/. I'm not using FreePBX at this time. Hopefully you don't need to port forward."
You would need to enable/set debug to check whether the respective packets are arriving. If they are then you may need to change configuration settings if they're not being processed properly. I'm not going to support FreePBX. I'm not using it.
If the problem you're describing is example 1, where the cellphone continues to ring despite hanging up your FPL phone, then you need to see whether CANCEL is being sent from your side and also whether 487 is coming back to you. I would see whether my router is causing a problem by testing without it briefly.