I think this is definitely singular. The XOR is actually a clue: the writer is expecting one or the other, not both. English "or" is logical XOR.
Consider, "If either your e-mail address or your mobile number has changed..." That sounds mildly wrong with 'have' to me at least. It's interesting that it's so marginal though.
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I think this is definitely singular. The XOR is actually a clue: the writer is expecting one or the other, not both. English "or" is logical XOR.
Consider, "If either your e-mail address or your mobile number has changed..." That sounds mildly wrong with 'have' to me at least. It's interesting that it's so marginal though.
Paul, native English speaker :-)