I've found that when I give the "Ms" answer, there is always a pause. Does make me laugh 
Asking for a title over the phone, I don't actually have a problem with. I also have to pose the question as a business, as otherwise how would I know how to address a letter? Sometimes, it could be Dr or Rev, or something else (male or female). I would not like to send a letter to someone just addressed as "Dear P Smith", for instance. A "Miss, Mrs, Ms, Mr, Dr, Rev", etc etc, makes the written communication more polite.
So I can understand that. For instance, I regularly receive a communication that says "Dear Evans". Now that makes me a bit cross. I am either a Miss, or a Mrs, or a Ms, or a Dr, or a Rev, or something else (in real life)
Were I to be asked in conversation (or on a form) for my marital status, then that would be another matter entirely and the question(er) would receive the appropriate response (coff coff), because that really would not have any bearing on that transaction
There are reasons why the question might be posed, and appropriate response provided. There may also be reasons why some might take offence at such questions posed, unnecessarily.
In short OP, I think YABU, just because you are assuming the person on the end of the phone is asking for your marital status, when in reality, they are just asking how you would like to be addressed.