The main reason for this sort of thing happening is a communication error between registry and registrar at the time of your purchase.
Essentially you try to register a domain, but for some reason the registrar can't connect to the registry's database list of "Premium" domains. So at that point the registrar platform assumes it's not a "Premium" domain and allows the sale.
Then at some point later when the registrar tries to reconnect with the the registry to complete the registration, the registry kicks back an error because the transaction was done without the correct pricing.
The actual specifics of the above can be a bit different depending on both the specific registry and specific registrar .. but in general it's 100x more likely to be a registrar<>registry data communications error than it is to be some sort of conspiracy of the registry and/or registrar to hog all the best names (they already did that ahead of time with their premium lists .. lol)
I think sometimes the "Premium" list is sent to and is hosted at the registrar, but even in that case there could be a platform<>database connection issue at the time of your transaction.
It's very important to remember that the bulk of back end platforms in the domain industry are extremely buggy. As much as I love GoDaddy for their great selection of expiring domain auctions, they've got sooooo many open and long-standing bugs/glitches that I probably couldn't count just the ones I'm aware of on both my hands!
Anyhow .. unfortunately I know exactly how you feel ... A few years ago (before I was a domainer) I found some great ngTLDs available .. I spent a good dozen hours researching, googling, and finally grabbed about 20 of what I thought were beyond amazing top-tier 1-word domains at NON-PREMIUM pricing ... the transaction went through .. but eventually got clawed back because of the reasons above.
I was SUPER pissed .. more at how it happened and the poor follow-up communication along with zero effort to try to find some compromise with the registry.
Hopefully
@Rob Monster /
@Sufyan Alani can use their industry position to get in touch with the registry in question to hopefully get you some sort of compromise/deal.
Good luck!