Let's not forget about their massive bill from HMRC, whatever happened to that story, not sure if that will be enough to fold them if goes against them. As in the linked thread, I had a fraud attempt on my card, my friend did a week after joining and they also overcharged me by £20, contacting them I just go a corporate "go away you're not a customer anymore so we can't do anything" response.
For EE signal, Spusu and 1p Mobile are popular choices and I see Mozillion now joined the party, only seem to have been operating for less than 6 months but if want to take a punt they are offering 100gb monthly data for £149, 24 month contract.
Lebara is one of the more popular choices with constant offers for Vodafone signal, TalkMobile is similar but they do a credit check (if that matters) when you take out their SIM plans.