I am on a basic plan (free) but got charged $199.67 on my credit card processed on 16 Aug 2021 can you please refund.
I have no 12 number transaction ID. I only have the following details on credit card 'Rxxbxb6T7S35Db.Tt/Cchelp le'
The 12 character transaction ID is right there in the information you included in your post; Rxxbxb6T7S35. Visit the link at the end of that ID (db.tt/cchelp), then enter the ID and other requested information to identify the account you're being charged for.
For further assistance, you'll need to contact Dropbox Support directly. Visit the Support page while you're NOT signed in to a Dropbox account, including these forums, and you'll see an option for Billing issues. It's best to use an Incognito or Private browsing session to make sure you're not signed in.
Dropbox cannot charge you if they don't have your billing information. If you've been charged and didn't give them your billing information, then someone else has and you should be contacting your bank.