Calendar app get hacked

I think that my calendar app is get hacked by someone, gives me notification that my phone is having virus and go to this link to clean your phone from virus. I ignored the notifications but now i am totally annoyed by these notifications. I think that the virus is programmed in such a way that in after a specific time it will replicate itself and gives me notification. My phone is updated with latest iOS update still my calendar app shows this problem. So what should I do now?