Buyback as in you bought it from somewhere, and the government buys it from you. Buyback doesn't, to me anyway, imply that the government sold it to you in the first place.
NOUN buyback (noun) the buying back of goods by the original seller. the buying back by a company of its own shares. a form of borrowing in which shares or bonds are sold with an agreement to repurchase them at a later date: "a share buy-back" synonyms: retrieve · regain · recover · get back · reclaim · repossess
That's simply "buying".
Your position in this whole sub-thread is very odd.