I had same problem with Croma, and my account was blocked my marking as business purchase. This was due to cancellation of few high value items. Cancellation was happened before shipping and in reality, I havent had purchased anything. I sent mail to unblock the account, but they said they can't do it. Even escalations didn't help. Today After 14 months, when I tried to purchase from Croma (Via tata nue) it worked. Directly Via Croma also working. It seems there is a time period after which the account will be unblocked.
I could have ignored this by using any other account, but tata nue automatically select this account associated with the mobile number, so it is important to get it unblocked for getting the nue coins.