Grow some balls and grandfather in the old accounts under the old conditions without limitation and let them die in peace or grow until they are good customers.
You don't wipe away a cock-up like this with a band aid solution, you wipe it away by going the extra mile. And if you can't go the extra mile because you really have to do this in order to survive (and apparently there was at least $60 play in there) then you should publish your figures.
Painful, but it will create the understanding required to make the merchants swallow the bitter pill.
I've mentioned a time or two that one of the benefits of charging more money is that it scares away pathological customers. A business which wants telephone support for their credit card processing systems integration and is not willing to pay $100 is virtually a textbook pathological customer.
(If it needs saying: I am a bootstrapper. I love boostrappers. Many of us are pathological customers with unreasonable expectations.)
And while bootstrappers may be misers they also know the value of a contract, even if it is in the form of the terms of service on a website and a price point they can live with, which they no doubt researched before signing up.
They understand giving timely notice and the reality of life for other businesses.
A 180 degree course change needs more of an explanation than 'we do this because we can', that is (far) more damaging than having some egg on your face for being overly optimistic.
I've messed up in the past, we gave out 'lifetime' subscriptions for $89.95 and we really made good money on them, for about 3 weeks. The way we plugged the hole way to stop selling them and to announce a sunset clause that said that if your account had been dormant for more than 12 months it would get deleted.
Not a peep.
That's how you deal with mistakes like this, not by suddenly tightening the noose.
(Apart from claiming that PCI was a benefit).
That's inexcusable for a service provider.
But some things are just 'not done', rearranging a deal after the fact is very bad for business, especially if you are in finance, where trust is everything.
After all, you are literally dealing with your customers money and their trust is the most important single resource you've got.
especially "fully coming out of beta in order to serve you better", because that beta logo really hindered the user experience
That being said, it's arguably an effective business move. Businesses that came in early have an uphill battle to switch providers -- many will stay out of complacency.