Dear Uday Ji,
First of all, if you are registered under any of the existing laws(i.e before gst) you have to compulsorily migrate to GST as per the provisions. If you were not registered under any existing laws due to turnover below threshold limit then you will be considered as new registrant under GST and you will not be required to take registration.
If you have already migrated under GST regime, then you will need to submit the application (FORM GST -29) for cancellation of the GST number within 30 days of the appointed day i.e. 01/07/2017
As per my understanding of your business, it is a B 2 C affair which means you would be selling the goods to unregistered CONSUMERS. The person selling to you will have no problem as you will not take the credit of the inputs nor the consumers will take credit of GST paid if any.
ONE Interesting point.
If you are registered under GST you will have to levy GST in your bills as threshold is mentioned only for Registration and not for payment of taxes as per the provisions. (unlike Service tax). Therefore, if you want to continue with the registration you can opt for composition scheme (1%) and stay clam. And if you do not want to get covered under GST then apply for the cancellation of the registration.
I hope the text is useful to you in some manner.
Thank you,
Mehak Malhotra