Please tell me if there is any cure for cystic acne?

Don't worry. Although the term "cure" is misleading for any chronic condition, the answer is yes, you can totally inactivate and prevent cystic acne with or without oral medications. It often times requires a tight relationship between patient and practitioner. This video may give you some hope: have a great day, -Dr. Neal Schwartz.
Serious Rx. You will probably need isotretinoin. This will keep it at bay for several months to a few years, at which time it will either self-cure, recur amenable to milder rx, or respond to another course of treament. Acne is a grave professional liability nowadays and although Isotretinoin isn't for the faint-hearted, please consider trying it.