GS 802 - VOIP.MS loosing registration


The registration keeps on getting lost so unable to receive incoming calls. This is the explanation I received from VOIP. Any one have an idea on what else I can check.
" When set a local SIP port in the device, the router usually tries to give that port to the device. If you have multiple devices with the same port, the router will give the port to one, and will make some kind of exchange in the port number for the other devices, something like a translation. In this case, regardless the port I asked you to set, the router is not giving that port to the device and is assigning a different port instead, as if the port was taken or locked. That is not the normal behavior for the router, and that seems to be causing issues with the connection here"