The rules appear to apply to "wireline" as well as "wireless" providers. I don't know if the FCC uses the term "wireline" to refer to something unexpected, but my best guess is that your experience breached the FCC rules.
There is a complaint link on that FCC page.
In particular, https://www.ecfr.gov/current/title-47/chapter-I/subchapter-B... has what seems to me like pretty strong language:
> 47 CFR 52.34(c) Telecommunications carriers must facilitate an end-user customer's valid number portability request either to or from an interconnected VoIP or VRS or IP Relay provider. “Facilitate” is defined as the telecommunication carrier's affirmative legal obligation to take all steps necessary to initiate or allow a port-in or port-out itself, subject to a valid port request, without unreasonable delay or unreasonable procedures that have the effect of delaying or denying porting of the NANP-based telephone number.
For wireless carriers, yes. I'm not familiar with any for landlines.
Edit: https://www.fcc.gov/consumers/guides/porting-keeping-your-ph...
Looks like small providers don't have to do any porting, plus as a sibling comment pointed out, you can't port a number after you cancel service.
In fact I had a case where I switched from Verizon without moving. But Comcast’s switching gear was in a different exchange so they had to change my number.
This was a while back. There may be more flexibility today.
So just don't tell your current provider, the new one should be able to handle it.
If your wireline carrier hasn't been (re)absorbed into ATT, Verizon, or Frontier, it might be small enough that there's no competitive carriers in their central offices.