According to the FIOS skill, you should be able to ask for a station by name. In fact, the skill description gave a samples of what you could say, "Alexa, switch to CNN" and "Alexa, go to NBC" and "Alexa, change to channel 899."
Maybe it just has trouble with ABC. Try some other station names such as the samples above.
One thing to note, your command was "tune to xxxx" and the sample commands from the skill description is "switch to xxxx", "go to xxxx", and "change to xxxx." I don't know if that makes any difference. It shouldn't, but who knows.