They are a registered charity, perhaps, exempt by law from teh DNC List.  YOU can kindly ask them to remove your number from their list and, maybe, they might.

Repeated calls, but never a message left.

They called me today and did not leave a message. I called them back asking to be removed from their list and they complied.  When I asked how long it would take to be removed from their list they said it would happen that evening.

got a call three times on Aug 30/31, no response on other end of line\
I thought when I suscribed to the no callers list, I would be exempt from this type of call
What gives?

One of the rare #'s when you call back it's actually them.Clearly, it's a rogue call centre or calling staff that's trying to meet a call quota, and their strategy is to call me, provide dead air, leave the line open from their end as long as possible, and get paid for it all. Just another problem that we've created in our world, and actually paying people for it.

Yep, this stupid caller call my number very often too.