To what extent does a person's oath by divorce affect his future actions related to transferring or purchasing phone credit, and does this include bank transfers, or purchasing from a grocery store for others, or for himself, or for his wife, or using another person's phone?

As long as the swearer did not have a specific intention in his oath, he does not break it unless the transfer occurs in the manner that was the reason for his oath. Consequently, he does not break his oath through the three scenarios mentioned in the question. We advise disregarding obsessive thoughts and not paying attention to them, as indulging them leads to evil and affliction, and ignoring them is the best remedy.