I’m being charged 12.99 for Spotify Premium. What is that? It charged me twice in a few minutes apart on today 9-27-2018
What is Spotify Premium? And why was I charged twice in same day. 9-27-18
Are you seeing the charge on a bank statement or have you received an invoice via email stating that you're being charged $12.99? I'd keep in mind that a lot of emails are designed to look similar to Apple emails in terms of content, pricing, etc in an attempt to get personal information such as your credit card number, social security number, etc. The articles contained below should help you determine if the email is legitimate in the even that you saw this via email.
Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support
Identify legitimate emails from the App Store or iTunes Store - Apple Support