Ported Number not working with iMessage

Hi.   I recently ported my (UK) mobile number to a new provider.   Since then, although my iCloud details on my iPhone tell me that the number is registered for iMessage and FaceTime (it wasn't initially and for a couple of days), it cannot be used for those apps - a revolving cogwheel appears on the left of the number in iMessage and FaceTime, instead of a tick.
I can of course use iMessage and FaceTime with various registered email addresses, but I want to use my phone number for these facilities, as always before.  I've tried all the recommended standard remedies - switch off iMessage/FaceTime, restart, reset all the network settings, etc. etc., to no avail.  If anyone here can help with this I'd be very grateful.
TIA
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Wilf