Duolingo family plan discount issue on iPhone

a message offering a special one off New Year 60% discount on the Duolingo family plan popped up while I was using the Duolingo app and I subscribed immediately. However, when I was billed, they billed me the full amount. What is going on?

I have applied to Apple for a refund and I’m waiting to hear from them, but I am wondering if I was scammed somehow

[Re-Titled by Moderator]