There was a purchase on my iTunes account that I did not make

if your knowledge of this does not just originate from some random phishing attempt mail claiming to be from apple

then I would contact apple if I were you Contact Apple Support

Hi

Go to the Email bill for this purchase down near the bottom click on report a problem.

Cheers

Brian 🇬-1F1E7;

No, No, No, No. Don't go clicking or tapping anything.