Awful phone lines with a muffled sound, you can barely hear what the agents are saying. Plus, their accent is so strong, that it becomes a huge obstacle to the communication. They also made loads of mistakes in setting up my SIM-only contract: they created an O2 account with the wrong email address (even though we had spent a lot of time over the phone checking its correct spelling), the SIM swap did not work (I spent a whole week trying the procedure over and over again), they told me over the phone to go to an O2 store, I went to 2 of them, where they were understaffed and told me to call the phone customer service back. Unbelievably frustrating. O2 seems to be crumbling down. I've already started to look for a new mobile provider...