I'm Demanding a Refund After PicsArt Billed Me Post-Cancellation

Even though I had previously canceled my PicsArt annual subscription through the App Store settings, $13 was charged from my account yesterday. Since I believed I had canceled the subscription, this charge occurred completely without my knowledge or consent.
Although I don't have an email or document confirming that I canceled the subscription, I did carry out the cancellation through the App Store, and despite this, I've been put in a difficult position because a charge was still taken from me. I haven't yet spoken with either PicsArt or App Store support about this matter.
I am requesting that the $13 charged unjustly be refunded to me, and that my PicsArt subscription be fully closed.