You may find all of this an excercise in futility. Generally, it is a waste of time to argue with JWs. Subjects like the "first and last" or the "alpha and omega" all have counter arguments that scholars have been discussing for years. Just compare the literature of the trinitarians with that of the unitarians. There is no point of agreement on the interpretation of these verses. Both present logical arguments. But both can not be correct. In the final analysis, each person has to decide which one thinks has the more scriptural basis.
Wouldn't it be better to thank the man for calling. Politely tell him that you appreciate his effort but that you believe differently than Jehovah's Witnesses and that you don't want to waste his valuable time.