Help! I just got back on after years of not playing and I have no champions!

To my knowledge, the last time I actually played was in 2016, but then my computer kicked the bucket, and I finally got a new computer this year. I read other problems similar to this, but I don't have the username problem. My account still has it's old user name, it still has the same level, player icon, and it even has the currency I had when I stopped. It still has a record of the top three characters I used . Oh, and it still has the alternate skins I bought too. The thing that's missing is...all of the champions! I don't have a single champ! Also, when I go to buy any of them is says that they aren't available for purchase. I don't know why this is happening, but I hope there's a good explanation.