CvW are you talking about problems with data or calls or both?
In my experience of O2 you can nearly always make calls most of the time even though you may only be connected to a very ancient 2G (G) 2.5G (E) or 3G (3G, H or H+) mast rather than 4G or 5G. However calls do seem to get cut off after a few minutes on very busy masts at peak times as though they disconnect the oldest calls when a new customer needs to make one due to limited capacity on the mast.
Data however is quite another story and I am now experiencing in rural Surrey, Sussex, Hampshire and Kent that most of O2's H+ (3.5G) masts that still provide data service to vast areas of the country outside cities and towns are now massively overloaded and you now either often get a timeout error in response to your request for a web page or a web page may take 20 or more seconds to appear. Also all through June, July and August I have been experiencing that in popular coastal towns like Portsmouth and Poole and Bournemouth that data services simply go off completely on all mast types (3G, 4G and 5G) and are totally unavailable once there are more than a certain number of day trippers in the area. So data services are often completely unavailable from say 11am to 5pm or 6pm for a lot of the summer in these busy coastal towns. And this is including the 5G masts in Portsmouth and Bournemouth/Poole, even though last year when I first got my 5G phone in May 2021 data services were available and quite fast on 5G most of the time in the summer.
The problem is that O2's arrogant and very sales led Spanish owners (Telefonica) have simply taken on far more customers with far larger data allowances (on O2, Tesco Mobile, Sky Mobile and soon Virgin Mobile) than their network was built to withstand and at locations that get busier at peak periods this is simply shutting down data services completely at those times of day.
I have been through complaints with O2 Customer Services and then to their CRT department (Customer Relations Team) who are supposed to phone you back but all they do is make a one and a half ring long call from 0800 800 0242 and then ring off each time before you answer (so they don't have to speak to you). I complained to customer services about this trick of the CRT team so eventually got a more senior Yorkshire based adviser in CRT who had been there since Cellnet days and he admitted their network was totally overloaded with data requests and my only option was to leave them if I wanted reliable data service. After this I escalated to the Complaints Review Service at O2, which was even more useless and simply rubber stamped the advice of previous advisers that I could not expect to count on O2 for data and should leave if I wanted a better service. As this made me pretty angry my complaint is currently with the Communications Ombudsman even though I have never taken any complaint with any organisation as far as Ombudsman level before.
There is no perfect solution as EE has faster 4G data available in more places but its signals don't travel as far from each mast on their old 2G and 3G cells or penetrate thick walled buildings as well as O2 or Vodafone's. www.rootmetrics.com shows EE has the fastest data service overall in the UK but EE has an appalling network in the area where I live and O2 and Vodafone have far more signal when I go out on walks locally etc.
As EE is very pricey compared to the other networks for the same data allowance currently I'm considering getting data/calls plans on Talkmobile (owned by Vodafone but cheaper) and Three and running two SIMs in my Dual SIM phone. That way I should have more chance of having data service most of the time although I will have to rely on Talkmobile for incoming calls.
See my other current thread on this topic at https://community.o2.co.uk/t5/Discussions-Feedback/O2-Data-Network-Unavailable-For-Hours-At-A-Time-A...
