Long story short, had a few SIMs with Virgin Mobile (stupidly). Numerous issues included push notifications not working when off wi-fi (had to manually open an App, e.g. WhatsApp, to receive the messages). Slow speeds (compared side by side with EE and they are not the same). Calls dropped... the list goes on.
On one occasion I asked to leave because signal was so bad in the house (before Virgin wifi calling). I asked the advisor 15 times to give me a PAC - she constantly tried new ways to get me to stay, including advising me to stand in the garden to make calls. I've been overcharged on occasions... and no one cared.
I've also had issues with Wi-Fi calling on Virgin Mobile - calls take ages to connect, can't call certain people (but can when I turn off wifi calling), people can't hear me when a call first connects... was easier to get a PAC by text than speak with customer services.
Though, as I mentioned, Virgin Media customer service is definitely better...