Of course, there's no historical evidence of this pact, no 50% off discount coupon, no contract signed on virgin human skin no nothing. What we have is a terrible natural disaster and a Prosperity Gospel adherent with an extensive history when it comes to making ridiculous statements.
There have been many responses to this, although none of them raise much above the level of calling Robertson some names and telling us why their faith is right and his wrong. I guess that's OK, if you're into that sort of thing.
My argument would be to go back to history, and see if there's evidence of said pact. Since there's not, we can all conclude that Robertson is just rambling on again and get on with the business of helping out those in need.
Don't let yourself get distracted by those looking to score a political point or two in order to better their own side through tragedy. Much like giving to political campaigns instead of charity, that's just a waste of resources. Focus instead on charitable giving to those in need.