They've just been hit by the UK regulator for massive shortfalls in their KYC processes. They were ordered to freeze accounts where the ID they'd gathered was insufficient for money laundering rules, and that turned out to be a significant number of clients, including, it would seem, you. While you might have provided everything they asked for, the point is that they didn't ask you for everything they should have. So while they might in general be prone to dodgy practises (i don't know), on this occasion I think they're being honest that they're overwhelmed with workload.