Help regarding LISP

I am a first year MBBS student.

I will enter second year in a month.

I have 2-4 batchmates who always make fun of my lisp (I had speech therapy & all, but still my voice is because of my thick & heavy tongue). I have 90%+ accuracy in speaking words, but those 2-4 people always make fun of me & mimic me behind my back. I feel very sad. What to do?