Sorry, you're too good to be promoted!

I've been working as a medical receptionist for 12 years and, not to sound obnoxious, but I work damn hard and am good at what I do.

Twice in the last 4 years I have applied for a different position in the same practice (from reception to costing and medical coding) and twice I've been told that the company cannot afford to lose me as a receptionist because it would be too difficult to replace me in reception.

Today I went for an "interview" at our head office and was asked one question and the rest of the time they told me, in a roundabout way, that they only advertised internally to follow protocol but that they will probably hire from outside. I am so extremely disappointed and frustrated. Does this seem fair? Should I just start looking elsewhere? I still have 25 years of work ahead of me but I can't seem to get the opportunity to progress and learn new skills at the company I'm at.