In terms of the Pricing page, there are two possible ways to deal with the problem. One, of course, is to fix the page. The other is to fix the pricing model.

I assume you've already given your pricing a good deal of thought, and have some reasons for having priced things the way you did, but off the top of my head, if it were me, I'd be offering pre-pay options, with steeper discounts for larger purchases.

In other words: something like 20 messages for $5, 50 for $10, 150 for $20-- and forget about the "monthly" plan altogether.

But, as I said-- that's just a gut feeling, without any real analysis. I imagine you know what you're doing.