Develop a credit card module -- 2

We have a website and we need to develop a module that will connect with a credit card vendor's API (NOT PayPal). There is already an API working between the two platforms, it should be a relatively straight forward process to build the module. We need a 2 way communication, so we get some info from the CC vendor and send some info to them using callback procedure (which already exists), so it should allow data transfer between both API's.

Programming language can be determined.
Additional info will be sent to potential candidates.