I have been with O2 on and off for roughly 10 years. Recently, their customer service has become terrible. You just simply ca't get through to a human being and often get left with an issue for days, or even weeks. I have been having an issue logging into the app and online portal for more than a year. I was first given some random email address to use as login. Then I was asked to register another email address to login. Just terrible. Not worth the hassle for a few quid saved. On top of that, my contract was £25 a month when I bought it two years ago. When I left earlier this month, it was over £34 a month ( a whopping 28% increase in just over a year as it became £34 just after a year). The only reason I rejoined two years ago was because they had a good deal through Mobiles.co.uk and their coverage where my house is is good, so I have 5G. I will do everything I can to avoid them in the future.