Have ed here doesn't make sense, strictly speaking. If the case is "we haven't called", ie, some fact lasts till right now, then this fact gotta start from a time in the past. Which's to say, usually it's always the past tense that works with since. Pretending the "since have ed" one was right, the only way to comprehend it would be: Now that I have moved to London, we can't call each other. Y'know, another meaning of "since".