Hi, My mums side is iyer, but shes married to a muslim( no caste ,converted 6 generations before).Mum has converted to muslim. I, the daughter who grew up with my maternal grandma, i am following hinduism.
When people ask me what caste i am, i dont have an answer, what should i say, should i give up being a hindu?
Your ethnicity depends on your dad's ethnicity.
If he is a Tamilian then you are are also Tamilian.
Your mother is a Tamilian as you have stated.
You were born to Muslim parents since your mum converted to Islam.
When you were born you surely would have had the Shahadah recited into your ears moments after birth..that makes you a muslim by birth.
Since you grew up with your maternal grandmum you are a practicing Hindu.
Caste isn't a compulsory identification.
You dont have to give anyone an answer.
As you said rightly that your dad's side does not have caste becos they converted 6 generations ago...that itself is your answer becos Islam doesn't recognize the caste system.
Just focus on being a good person which I feel you already are.
Regarding your choice of religion..thats purely up to you.
You dont have to give up being a Hindu just becos you cant classify yourself into any known caste.
Hinduism isnt about caste.
Hinduism is about transcending all bodily identification including caste.
If you like Hinduism stay on..if not you can always explore Islam.
If you dont like both choose something else that makes you happy.