How do I withdraw a paper from a journal after it was accepted but before it was fully published?
Check out the journal’s policy. While they do not always address the issue of what stages a paper can be withdrawn, you can find some indirect information. For example, if the policy says:


  Manuscripts for which page proofs are not returned in a timely manner will be withdrawn from publication.


(here in the case of the JACS journal), then you can still withdraw the paper at the proofing stage.
Leave a bit more time to the editor… it's a time-consuming job, and he might just be very busy. You can send a gentle reminder. Just mind that you are the one asking for something out of the ordinary, so mind your manners.
Where are you at in the publication process? If you have signed the copyright transfer agreement, paid the processing fee (you mentioned one; no all journals have them) and sent back the final proofs with your corrections, you might just be too late legally speaking. It probably doesn't hurt to ask, but you might not have legal recourses apart from retraction (and avoid that).
Whatever you say, don't ask for retraction. Retracting a paper once published is a grave decision to make, and it is not appropriate in your case.