Detailed twice in 12 hours

Pretty pissed off right now. I've been playing since beginning of January and got to level 15 two days ago. Had the box come up saying I'm going from 20 to 15. Played until 12 hours ago and reached level 13. I've just come on and I'm level 15 again. Even though I was level 13 when I left this morning What's this? Is this what happens with this game?

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