@Korbs I can't see that having anything to do with O2.
Have you tried resetting your phone?
Right so I payed my phone bill late and got cut off. It’s now all payed up and my calls, data and text are back. Whilst it was cut off the loudspeaker option is not highlighted and I cannot press it, I also cannot hear anything and my microphone is not picking any thing up. Does 02 have the power to stop my microphone if so, will it come back on? Any fixes? Has anyone else had this problem? Before I considered it being my actually device which is a iPhone 7
Its your device not O2. Suggest restarting. If that fails a re set should sort it.
Make an appointment with Apple https://www.apple.com/uk/retail/geniusbar/