Your anaytics will tell you where you are losing people if it's set up right..
If you have the same number of overall visitors to the 'shopping pages' not just the website Then you need to see how many are adding to cart now vs then. Then you need to see how many add to cart and then never pay (cart abandonment) Those numbers will tell you a lot about how people are using your site.. I would wager that your conversions are down not because of accepting credit cards (unless you have that configured wrong or it's very hard to use)..
Have you purchased something from yourself to make sure that it all work?
It is possible that the design change from the old to the new pages has confused your buyers enough to make the purchase channel break..