Lvl 20 and no access to Tier 3 Runes?

I just picked league back up, haven't played since Season 3, so I'm having to relearn everything. I went from 17 to 20, hoping to use Tier 3 runes to my advantage, but now that I'm here I can't buy them. The shop clearly states that I need to be Lvl 20 to buy them, but they're treated as locked despite my current level status. I'd appreciate help in alerting RIOT to this issue. Please fix this, it's a big issue for those who save up IP and look forward to Tier 3 runes. I can verify that this has been an issue since 2011, because I've found some discussions from 4-5 years ago, complaining about this issue.