Hello, I have recieved a caution advice notice just a few days back from my bank(HDFC) mentioning all my bitoin transactions dated back to 2013. Has anyone else noticed similar notice? It also said ""revert within 30 days from the date of this letter or the bank will be constrained to restrict transactions in your account without any further reference to you"". Does that mean I have to write them back?
Yes. If you want to continue using your account, you will have to respond to them.
They probably will highlight their terms and conditions and allow you to continue using your bank account. You haven't done anything illegal.