I ran into a similar issue regarding not being able to send ^C (Control-C) to through the telnet session. Additionally, I was getting serial over the telnet session and there was a echo each time I interacted with the terminal. That is when I entered "a" in a linux bash shell I'd get "a" back twice and a "a: command not found" or I'd get two prompts back upon that is: $ $

I resolved this issue by ensuring the telnet session I was using was configured to use RFC2217 protocol. This corrected the anomalies of the serial terminal and the echos and "control" characters were properly interpreted. See https://tools.ietf.org/html/rfc2217

I ran into a similar issue regarding not being able to send ^C (Control-C) to through the telnet session. Additionally, I was getting serial over the telnet session and there was a echo each time I interacted with the terminal. That is when I entered "a" in a linux bash shell I'd get "a" back twice and a "a: command not found" or I'd get two prompts back upon that is: $ $

I resolved this issue by ensuring the telnet session I was using was configured to use RFC2217 protocol. This corrected the anomalies of the serial terminal and the echos and "control" characters were properly interpreted. See https://www.rfc-editor.org/rfc/rfc2217