Hi friend!
1. The firewall does not open the Telnet service by default.
2. There are two ways to turn off Telnet: the undo telnet server enable command is used to turn off the Telnet service and prohibit Telnet users from logging in. The telnet server disable command is used to disable the Telnet service and prohibit Telnet users from logging in.
3. If Telnet is turned on or off at the same time in the global and interface, the interface has priority.
Hope this helps!