Nighthawk R7000 - Block incoming IP address OR How to block SIP Scanners

We use FreedomPop, but it could be any VOIP service.

One phone has been getting calls almost "non-stop" for several days, when the phone is set on wifi service.  They are from non-standard phone numbers 100, 101, 1000, 1001, etc.

FP says that since the call is not coming through their servers there is nothing they can do about it.

Googling "SIP Scanners" and voip, 101 phone calls, or other related searches, the best advice seems to be to change the phone's SIP port from 5060, or block the IP addresses at the router (from the logs, about 20 such addresses so far, almost all are IPs from Europe/Asia).

There is no option to change the SIP port from the Android phone (it is greyed out).

Netgear R7000 doesn't have IP blocking.

Tried Port Forwarding, but don't know if it would work, or if I did it correctly for the intended purpose, the "xxx" being the IP for the phone...

Service Name:  IP Phone

External Start Port:  5062

Internal Start Port: 5062

Internal IP address:  192.168.1.xxx

Seem to still be able to make calls and texts after setting this .

No annoying calls yet from the SIP Scanners, but they do seem to take a break and "randomly" pick up again.  Might be in that lull period.

Have been placing the phone on 3G/4G mode in the interim to avoid the SIP Scanners, but that eats into minutes and texts.

Would appreciate confirmation that the above is the right way to go and it is done correctly (i.e. that there no unforeseen screw up in the service to be discovered later, or that this lull isn't just kidding myself that it "works").

Thanks.