IPhone 5s isn't receiving messages on time?

I don't use or want to use iMessage.
I'm with Optus prepaid, I've also had my phone replaced assuming it was the phone having problems but even the new phone is having issues. I have switched it off hundreds of times, restarted it and restored it.

It's a really difficult situation, I don't understand why this is happening. If anyone could help me, that'd be great.

Only your carrier can answer that

As suggested by James82, i would advise the same

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