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: | 308 |
| Nodes: | 10 (0 / 10) |
| Uptime: | 00:04:40 |
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128 files (25,814K bytes) |
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