Incredible amount of issues with port forwarding.

Hey, so my family recently switched from AT&T to Xfinity due to pricing, and now I am having very constant and consistent issues regarding port forwarding.

For context, I am trying to port forward for an Arma 3 server and a Teamspeak server, for my friends. Port forwarding worked perfectly on AT&T. It also worked fine the first week on Xfinity, after port forwarding. The second time I ran a server on Arma 3 and Teamspeak, i had to troubleshoot for three hours until I restarted my modem (TB7) and THEN it worked. Now, I have restarted my modem three times, and has not worked. Second of all, I cannot even delete my port forwarding settings, as when I click delete port forward, the port forward stays on the app. Please, any help is appreciated.

EDIT: Ok so I found how to fix it from this thread on Reddit: https://www.reddit.com/r/Comcast_Xfinity/comments/15mmufi/port_forwarding_disabled_permanently_for_xfi/
Basically, you use the "reserved IP" you get in the XFinity app on your phone, and from there you go to the control panel app on your computer (assuming windows), preferably the older looking one not the shiny one Windows uses now, for some reason that one doesn't let me change IP? and then from there you go to [Network and Internet] >> Network Connections and choose the network device your computer uses, go to it's properties, double click on "Internet Protocol Version 4 (TCP/IPv4)" and set to "Use the following IP address", entering the "Reserved IP" in your xfinity app, and finding the subnet mask by going into Windows CMD and typing ipconfig. Press ok twice and atleast for me, that worked.