Ever buy anything on ‘layaway’ or any similar arrangement? If you’re handing over money, but not getting the goods, you’re probably doing something wrong. The vendor has your money, but doesn’t have to provide anything in return. You don’t have your money, or whatever it is you’re buying.
Try this: Instead of making payments to a store, make them to yourself. Put the money into an interest bearing account (preferably something like one of the online high-yield savings accounts). It will make you more money while it’s sitting there and when you have enough saved up, go buy what you want.
That assumes, of course, that you have the discipline to leave the money in the savings account and not spend it on something else. If you can’t do that you’d better learn how, or you’re never going to be able to get a handle on your finances.