I have an iPhone X running latest iOS 11.2 and over last few weeks sometimes phone will not ring but get a text saying missed called most times I call straight back no problem and have a decent signal. Just spoke to O2 they told me switch off do not disturb completely I only had it on on scheduled between 10pm and 8 am but have been told it needs to be off as this is an know problem with iOS anybody else have if this or are o2 talking rubbish