Door Lock Help? Prevent Credit Card Entry without Deadbolt?

I have a lock that requires a key, similar to one you would find on a house door, except I dont have a deadbolt. Installing a deadbolt is not an option-it is a bedroom door and I am not allowed to install one. My brother has just recently figured out a way to open my lock with a credit card......How can i prevent... show more I have a lock that requires a key, similar to one you would find on a house door, except I dont have a deadbolt. Installing a deadbolt is not an option-it is a bedroom door and I am not allowed to install one. My brother has just recently figured out a way to open my lock with a credit card......How can i prevent this? I'm open to adding nails/screws/whatever around the metal plate on the door or the door frame...pretty much whatever it takes other than buying a new lock. I'm not trying to keep my parents out-they have a key to my room as well. I just want privacy from my siblings, which I have had for a long time until recently....Any help would be appreciated. Thanks
Update: I'm 17....
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