Well, to be fair, I said that I don't know if I unsubscribed or not. But that is not really the point, though you guys do seem a bit eager to penalize customers for doing so. Your policies are your choice of course, but they seem short-sighted, and out of step with most of the software industry these days.
Few people are more enthusiastic about supporting small developers than I am, and I have put untold $$$$ toward my belief that those who provide good value should be rewarded, including a fair amount to X-Aviation. Rarely if ever do I balk at or whine about their pricing structure.
But I do not enjoy paying full price for the same product twice, especially given the first one was never really finished to its promised potential. If X-Aviation had said, "well the $15 promotion is over, but we do have an ongoing upgrade price of say, $40" I would not have hesitated - I happily pay upgrade prices all day long. This is what most of the industry does, because they're looking at the bigger picture, and truly care about rewarding and retaining customer loyalty.
I used to really like X-Aviation (as demonstrated by repeated purchases), but this is leaving a real sour taste for me. Again you polices are your choice, but I'm not sure you can really know the true cost long-term of this philosophy.