I downloaded Whatsapp but when ppl send message to me, it doesn't push and I have to manually go to the app each time and wait for messages. How to fix it? Tried removing and installed again. Doesn't work.

And, currently using maxis line, if I wanna change to digi sim card, will it corrupt my Whatsapp and ping account or will it just don't receive messages until I replace it with the maxis sim card back? Thanks.