Just my own experience with middle eastern airlines, don't bother with the call center. They tend to be staffed by low cost third party national labor who has zero authority to do anything outside the box. Find out how to contact the TUN sales office either by email or telephone and talk to them. I can't promise you that will work with SV, but it does work with RJ and WY.

Have your alternatives ready when you speak / write to them and tell them proactively you'd like xxx routing which still gets you to your destination on time.

I'm slightly biased but would take QR over TK, but TK is definitely a good experience as well.