InshAllah remain calm and do not let that individual degrade you like that. simply ignore them or either speak a word of justice. or simply say, "May Allah guide you". I don't know, whatever seems right so long as it is within the islamic guidelines. don't retaliate - this is not of the sunnah of our Prophet s.a.w. What these individuals say will not change the real you or who you are. You're a Muslim, and that's the greatest blessing of all. There's no need for you to feel angered, instead i pity the individual who said this to you because they've earned bad deeds in their book which the angles record in. subhanAllah.