unlocking my iphone

its sad I payed over 200.00 for a iPhone 6 and its a prepaid severs and they will not unlock it 4 me they say I have to be on the prepaid plane 4 6 mounts be4 they will unlock it I think that is bull if some one pays cash 4 something they should unlock it no matter what plan that it is on because it yours to what with and att will hold your phone hosted be4 they will do anything I have talked to 4 att sales reps and they sad that att will unlock it no matter what as long as its payed 4 they sad just call them up and they will unlock it 4 ya well that turns out to be bull as well so I have a phone that if I what to move from att on day and find a new carrier I cant do so because they have me locked in I like att because they have grate severs and prices but I don't like to be locked into something like a locked phone