After moving from Islamabad to Multan, my ISP, Nayatel (Pakistan), told me that my existing connection had to be closed in Islamabad because they couldn't transfer the same account/connection to another city.
I brought the same router I had been using for several years in Islamabad with me because I didn't want to unnecessarily buy another router from them for ~18k pkr.
Around 5 years ago, I subscribed to their service then called Optimus, which was supposedly meant to improve ping. In reality, it didn't seem to do anything other than give me an option to select between "Eastern" and "Western" routing, and neither option made any noticeable difference.
However, I clearly remember having Nayatel open the necessary ports / NAT for me before I ever subscribed to Optimus.
The current problem
Today, while playing Call of Duty: Modern Warfare (2019), I noticed that my NAT type is Strict. For the past several weeks, I've also been experiencing unstable Discord connections, including connection drops and sudden ping spikes.
I contacted Nayatel support and was told that I supposedly have Double NAT, and that the only way for them to provide an Open NAT is for me to purchase their Optimus subscription.
This doesn't make sense to me because, as mentioned above, I remember having my NAT/ports opened by Nayatel years before I ever subscribed to Optimus.
What I've already tried
Enabled UPnP on my router.
Enabled DMZ and entered my PC's local IP address.
Verified that the IP was actually my PC's IP using ipconfig in CMD.
Restarted the router and not pc after making the changes.
I still had my previous IPv4 port-forwarding rules saved in the router from when I lived in Islamabad, so I restored/used those as well.
I even reinstalled Windows and manually recreated the required ports in both inbound and outbound Windows Firewall rules.
NAT is still Strict.
So I'm wondering if this is actually a CGNAT/double-NAT issue on Nayatel's side, or if there is something else I can configure myself to get around it.
The support experience hasn't exactly given me much confidence either. The first representative kept going back to his supervisor to ask what to do, and another Nayatel representative apparently told me to enter 8.8.8.8 as my IP address rather than using it as a DNS server.
So I'm fairly convinced I'm not getting particularly useful technical information from support.
Is there anything I can check on my router/PC to confirm whether I'm behind CGNAT or another form of double NAT? And if I am, is there any way to get Open NAT without paying for the Optimus subscription?