I know there has been a concern about Helix and their invoice payment issues. I, too have been caught up in this mess. But, in a timely fashion, the support from them in this matter has been exemplary.
Their service they provide has been reviewed before, but the ticket support hasn't received a fair shake. All it takes is a little patience on the end user part, and they bend over backwards to keep your business.
Recently tried to pay my invoice. There is no chance i'm entering in credit card details for a normal card into a payment gateway that i've never heard of and using a pre-paid card gets rejected.