iPhone not receiving messages from android devices

I have noticed in the last couple of days my phone will not receive sms messages from any android device. Then 24 or 48 hours late the message will come through.

I have gone through all the recommended troubleshooting fixes, i.e switching phone off, deleting contact and messages, resetting networking settings, checking to make sure the contact isn’t blocked, ensuring that mms messaging is enabled, turning iMessages on and off.

i have checked my network and it is working fine.

i am not really sure what else to do??