At times, it can be redundant, but you could try one more time.
Assuming it's Windows. Download search everything, and install. Uninstall steamfab. Use search everything, searching for just the word streamfab. Delete any folders/files found.
You could also instead do what it says (here) to do a 'clean' uninstall.
Download the latest version of SF and install and try once more.
Look hard enough, you will find a VPN or proxy cheap and buy for one month to try that. Many VPNs, are less than $30 a year, and easily as low as $5 for one month, by looking for discounts.
You may even come across some free proxies, but the free ones are limited, but that might be enough for what you need.
You can try if you're a bit more tech-savvy trying to change your ipv4 and ipv6 DNS servers, a few times that helped, reference (here)
From what Germania is saying, it might be something similar to Netflix, and a VPN is the only thing that worked constantly for me, with logging into Netflix. You only need to connect to the VPN, then log in to Netflix, then disconnect the VPN so as not to cause download issues.
If not, if you try posting a log (I doubt that will show much, but you never know), or contact SF feedback and move on, because it will be months before you get any relief from SF feedback.
You could also check with others who have your ISP to see if it's easy to change your IP, Sadly Xfinity locks it to the MAC address of their rented Modem/Router so the only way for Xfinity users to change that way is to swap out modem/router, which would then have a different mac address, and then you will get a new IP. Years and years ago when Xfinity only offered a modem, not the combo modem/router, you could easily change IPs.
As always, I wish you and other people luck because it’s a very small handful of users saying any login issue for Paramount+.
And also it doesn't matter if browsers log in, It is something still, at times, with the SF specific browser that seems to get blocked from logging in for a set amount of time by IP or similar.
Although if it really was 5 days or more, that's an unusually long block.
