It's pretty simple. Zombaio isn't technically a credit card processing company from what I understand.
For a company to accept payments on behalf of other entities, they should be going through the regulatory / accreditation process of being a PSP (Payment Service Provider) or IPSP (Internet Payment Service Provider) in the eyes of Visa or Mastercard.
Read the top of this page:
https://www.visamerchantagentslist.com/ - it sounds like if you were going to use a company to handle payments on your behalf, you'd want them to appear on that list or appear on the list the US region puts out. CCBill, Segpay, Epoch - all can be found on that list.
Zombaio.. nope. Zombaio is nothing more than someone who started a company, with what I will label a "creative" way (others may describe it as shady) to handle payments on behalf of other people, but didn't actually want to do all the work of doing things correct (Because its a lot of work and a lot of $$), which is a very risky situation, which is clearly documented with late payments. And if they go out of business, and you cry to Visa & MC, they are going to say you should've done your homework and not trusted a company who was never accredited by them.
Bottom line, their rates might be attractive and you might be skirting all these other fees but there's a reason to the madness. If you take your business seriously, you should just use an accredited biller, or get a merchant account. When youre payng the registration fees via the other accredited billers, think of it as "protection" money. There's a rule, you comply. You want to break the rules to save a little bit of $, don't be surprised when you lose a lot more because a company chose to go a different, albeit cheaper route. I felt the need to post this because of what the OP posted.
Impossible to run a real business when your payment provider isn't providing consistent payouts.