Does Spectrum block attempts to connect to the FTP server on the tp-link Archer c7. My FileZilla log has this response:
Status: Connecting to 172.27.35....:21
Status: Connection established, waiting for welcome message...
Error: Could not connect to server
Did you already have static IP / and DNS manager service setup, And don't forget port forward to the FTP IP. Have you tried SFTP instead?
FWIW, one common way to shift a two digit port is to simply put a prefix of 10 ahead of the two digit port number, so 21 becomes 1021, 80 becomes 1080, etc. An alternate method is to enter the two digit port number twice, so you would get 2121 and 8080.