15" BBS Split Rims

Hi everyone, as you can probably tell I am new to this forum!
I have a VW Mk1 Golf Klipper 1989 model that I purchased this time last year. It came fitted with the aforementioned Split Rims and I am, hopefully, taking them to be refurbished next week. So I tried to take a wheel off today and failed miserably! I have the special black plastic tool to undo the centre piece however all four wheels just keep turning and turning! Ive tried to 'snap' the centre in order to try and undo and I've turned slowly to see if I can feel a point which would allow the removal. Ive avoided the temptation to place a covered screwdriver to prize the centres off.
So, any advice?
Thanks in advance.

Hi mate
When I had my BBS I just twisted and pulled hard and the centres just popped out pretty easily,I has BBS 012 on mine 
Cheers
Neil

Thanks Neil.
I am sure it is going to be something simple but it is proving rather tricky!
I assume you didn't use the black plastic 'hex' tool? Just hands?

Yes mate just my hands never used hex tool as it would just spin round,just gripped the centre hex and twisted and pulled hard or can you push the dimpled ring in so pops off so you can get more purchase on hex from behind. 

Need to know which BBS they are but if they're RM's they'll have a "dimpled" ring around the outside of the centre hex nut, if that's them then the ring comes out with the centre nut all as one part, try a set of plastic pushbike tyre leavers in the gap between the ring and the rest of the wheel and they should pop straight out towards you

Thanks everyone - done it!
Apparently the centres on these simply 'popped off' as oppose to undoing with the 'hex' spanner. This, quite evidently, was a bit of a red herring as the spanner was supplied with all the bits and pieces in the boot when purchased.
Anyway, resolved. Thanks guys for your support and speedy responses, impressive.
Adam.