No mastery lvl6 token

Hi there, I've been mastery level 5 on Lulu for a couple of months now, and today I finally got an S- on Lulu, but I did not get a mastery 6 token. It is not in my loot. When I look at champion collection and hover over Lulu, I see: "Season highest grade: S-" "Rank S- or higher to earn a Mastery 6 token. Combine 2 tokens to advance further." Why is this and how can I get my mastery token? Because I would like to get to level 7. Thanks in advance. Mikasa420