How long do Royal Mail take?

So this is what happened, I had my phone fixed by my phone companies service center Sony Ericsson, 10 days later they sent me an email telling me that they have fixed it and quality checked everything.

So they send me another email on the 16th telling me that my phone has been dispatched on the 16th of October which was Thursday and it will arrive the next following day.

So Friday went passed and they didn't deliver it,

Saturday went passed and they didn't deliver it

Its Sunday so i know they don't deliver stuff on Sundays right.

So will it come on Monday? If it doesn't what should I do?
And Should I go to my post office to check if its there and should i ask my neighbors if they have signed for it.

And what time do Royal Mail usually take to send packages like my phone??

Thanks in Advance