I have been charged 49.99 on my Apple account and I don’t know what it is for

If you're sure that those charges come from Apple (check your bank statement very carefully, ignoring scam messages that might be addressed to your iPhone), start reading this support page:--> Subscriptions and Billing – Official Apple Support, and check each of the first 3-4 sections.

If you cannot find the information you were looking for, please contact iTunes Store Support Team directly and explain your problem, using this specific link:--> Apple Support

Regards

Giulio