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: | 319 |
| Nodes: | 10 (0 / 10) |
| Uptime: | 01:08:21 |
| Calls: | 2,670 |
| Files: | 6,522 |
| D/L today: |
49 files (22,798K bytes) |
| Messages: | 491,112 |