Just to be fair. I did get back my refund ($672.80) for unused credits within 5 business days from Propellerads. A different case from OP I guess.
I am doing a lot of blackhat stuff using propellerads so my advice is to use them if you know how to cloak well. If you intend to do white hat campaigns, better stick with Google, Bing, Taboola, etc, The bigger traffic network.
White hat will not give you a good ROI from Propellerads, so don't waste your time on this. This being said, some members here could be running a profitable campaign on white hat with propellerads so I might be wrong about this.