Their deposit bonuses seem to good to be true anyway.
That's because they were!!!
£1200 in BONUS account, 20x WR slots and 60x the rest. only WINNINGS above the £1200 could be kept, and once transferred the £1200 bonus was confiscated.

Now though, it's a different matter. Bonuses put in REAL account with same WR, but everything can be kept once WR is met. Meeting WR can also lead to more bonuses (more WR also), while original WR is met.
Meeting WR in the daily tournaments is possibly best bet. Do NOT cash in the rewards until you reach Platinum VIP, as they are worth 4x as much and are carried (assuming you want to continue to play).
Best to ask support what the problem is with the security check. It may simply be that now you want to play for real you are being subjected to the usual checks. You should tell them your new address and E-mail, and ask what documents are needed to enable use of the Instant Payments facility.
They will most likely want a photo ID issued by a recognised authority, an image of the front and rear of any cards used, and possibly a deposit declaration form. Any more than this is not "routine" but an indication that your account has been flagged for potential fraud risk, but this might simply be because they think someone has stolen your identity and is trying to use it to open a real account from somewhere they know you don't live at (unless you told them beforehand).
If you feel up to £/$1200 at 20x on slots, possibly worth a try clearing this up.