After being in touch with CS here’s the story:
The account wasn’t fully closed because an offline transaction from Ryanair presented after I got e-mail confirmation that the account was closed. I’m actually surprised this is possible, and it leaves me a bit concerned - what happens if my card was skimmed and someone goes on a shopping/ATM spree on offline terminals - will I still be liable on it until I report it as fraud?
Where I believe Starling failed hard is that I never heard anything about it ever again - no e-mail, no call, no debt collectors (), nothing.
The other issue is that I’m now trying to log into my account to check out the transaction (as well as get the sort code/account number to pay off the outstanding balance), but given I’ve deleted both the app and the password, I am now locked out. There is no password reset option anywhere in the iOS app. CS assured me yesterday over the phone I’d receive a link, but so far nothing. Calling today they put me on hold and then apologized for technical difficulties - presumably the account being in an inconsistent state is crashing the web interface of the advisor.
Overall I’d still recommend Starling compared to any legacy bank, but this experience leaves me a bit disappointed compared to another fintech I bank with. Probably won’t happen to anyone else but I would’ve still preferred them designing & testing the app with edge-cases in mind before going to production.