It would ultimately be up to a judge to rule on whether any statements constitute an admission of the legitimacy of the debt, and thus might act to reset the running of the statute of limitations on the asserted debt.
However, I dont see how simply referring to the debt upon which they are calling is in any way an admission as to its legitimacy.
I would be confident, if need arises, to simply state that you were only referring to an asserted debt, and had no intent of admission to its legitimacy.
