If you take a look at this webpage about blocked ports, you'll notice that Spectrum says nothing about blocking port 23 but they do:
https://www.spectrum.net/support/internet/blocked-ports
| Sysop: | deepend |
|---|---|
| Location: | Calgary, Alberta |
| Users: | 281 |
| Nodes: | 10 (0 / 10) |
| Uptime: | 37:20:19 |
| Calls: | 2,402 |
| Files: | 5,169 |
| D/L today: |
59 files (17,647K bytes) |
| Messages: | 438,023 |