Did you find out where that 1.1.1.1 DNS server came from? How did you get rid of it?
Your clients (at least your Windows one) are still not using Pi-hole as DNS. Judging by its IPv6 prefix, that's rather another device from your local network most likely your router.
Your router may offer itself or your ISP's servers via IPv6, and also some router models (like ASUS RT-AC68) are known to distribute themselves in addition to any custom DNS servers, no matter what you configure.