Q: Why am I charged for a trial of 3 months of iTunes?

When you take up the three months trial of Apple Music a small 'holding charge', usually a couple of dollars or so, is placed on your credit card to check that it's valid. This won't actually be charged and will disappear. If in the end you are charged before the three months is up you should contact Support as it would be an error. To do this, go to https://getsupport.apple.com . Click 'See all products and services', then ' 'iTunes', and then 'iTunes Store', then 'Purchases, Billing & Redemption'.

iTunes Store & Mac App Store: About payment card authorization holds -  https://support.apple.com/HT201292