Hi @MDarwish
You can apply following security checks to prevent this issue.
1) Ask a security question and answer to your interested subscriber at the time of demanding News letter. Then ask the same security question again when any one tries to unsbscribe.
2) Send a OTP (One time password) to the registered mobile of your interested subscriber at the time of Unsubscribe. and then varify it before unsbscriber. If OTP match unsubscirbe it otherwise Failed.
3) Ask some personal details of interested subscriber (like date of birth, hobbies etc) at the time of Unsubscribe. If personal details match unsubscribe it otherwise failed.
4) As the @Mudassar sir suggested ask user to login again to unsubscribe.
Happy Coding
