TFS and every OTS engine I saw is 100% legal. We (community) created every engine from zero and we published it under free, MIT or GNU licenses in most of cases. Also every OTS engine is not using any kind of asset from Cipsoft.
OTClient is 100% legal. Idk who created it but it's distributed as a free to use software. In this case it's exactly MIT license (free). And it's not using any asset from Cipsoft.
Even using official Tibia to connect to OTS is NOT AGAISNT Tibia Client's license. I have no idea who was the first who said that. It's maybe against local law (Germany law) which applies to everything and everyone who is in Germany territory for example.
From Cipsoft legal documents:
"We do not ensure continuous, error-free, secure or virus-free operation of the software, the game, or your account."
Using any website made for OTS isn't against law. Same as with OTS engines. We made them from zero.
Using web graphics taken from official Tibia may be against, becouse we don't know under what license thier web grapics are. So in this case you cannot use them.
Name 'Tibia' as a trademark:
The most funny thing is Tibia wasn't a trademark for years. From 2010 or 2012 (based on info they sent to you) it is a registered worldwide trademark.
What they said to you:
Your website ... is infringing on copyright-protected material. The original website ... CipSoft owns the exclusive copyrights ... The unauthorized ... copy is located at: kivera-global.net The “Open Tibia” serverKivera-global"
So what you should do:
1. remove Cipsoft's graphics from your website. You can change it to something else. Take a MS Paint and do the job.
2. if your website is using a copy-paste html/php/js/css stuff from cipsoft then you have to change it too.
3. remove name Tibia from your game. You can keep using OTS.
4. send mail to OVH or your actual hosting that you don't have stuff they said. NEVER SEND MAIL WITH "I REMOVED WHAT YOU ASKED FOR" Becouse it will be a extra proof where you agreed, you admitted that you had thier graphics. It may be a shit proof but why they should have it?