Hi there, I have already purchased 3 codes, Tier 3. If I want to purchase 1 more it appears I go into one of my redemption codes and click "Get more codes" and then would I just purchase tier 1 to get one more code? When I try to purchase Tier 4 it makes me pay full price and not the difference from the 3 I've already purchased, so I need help with this please and thanks!