You don't understand Karby's post.
You have a bill for 26.90 per month, you just said that. You buy 3000 crysta. That means each month you have an extra 310 crysta left over. Well, you have a choice next month, you can either buy another 3000 crysta or 2500 crysta. If you buy 3000 crysta, you will have 620 left over. If you buy 2500 crysta, you will have 120 crysta left over. Either way, you still have an account for the 2 months.
Sure, over 4.1 years/50 months, you will pay exactly 1345 dollars, but you know what, so will I. So will Karby. So will anyone else who plays this game.