Simple Payment Card: Retailers Refuse To Pay

I just recieved a 'simple payment card', 3 different paypoint retailers refused point blank to let me use it to withdraw cash.

I have £800 approx in the account which is months worth of backdated esa, I cant get at it, not had a penny since 8th august.

Do retailers have any duty to pay?
if not, in the extreme circumstance of none of the retailers wanting to pay - what can you do?

Thanks for reading.