I honestly thought that these were current, since they are the ones I use, and the ones that the dashboard tells me to use.
But looking at several other sites on the ns1.byte.org - ns5.bite.org, no others that I can see are showing the infinityfree name servers. This would suggest (to me at least) that its not the name server thats reporting incorrectly.
Honestly, sounds to me like tenten are kicking the can down the street.
Although, its probably worth fixing the error500 first, since fixing that would allow you to better assess if there are any access issues with your site.
The other thing that might be worth looking at is using cloudflare (and their nameservers), which allows you to add protection to your site aginst DDOS attacks