Intex Aqua Star 2 — Phone trouble

Hi im using the intex aqua star 2 from may 2015 and it was quite good, there werent any issues. off lately im facing issues like contacts not showing, sudden disappearing of contacts, not showing on watsapp either. now my video recorder too has stopped working. both the normal as well as watsapp. to add now it suddenly goes blank while using and says android has stopped working or something.then the screen just goes off and i have to remove the battery and put it again and restart only then it starts.while on a call the recording starts automatically when i dont need it or suddenly it will go on mute o hold. what is this nonsense one by one something or the other is happening. please rectify asap.