"Nous voulons notre argent et les intérêts."
if 'interests' means interest or appreciation on an investment, then it is just singular.
I'm not sure: if you had several accounts, and they owed you interest for each one of them, how would that be expressed? And how about the French, is it always plural there?
I would imagine that the account holder would say, " We want our money and the interest from our accounts." I can't imagine anyone saying 'interests'.