This happens often here and if your trademark is in pending status, brand registry team wont help. You can buy a test product and submit to seller central & on forms they provide but it usually takes 15-30 days for this to resolve.

The simplest way to resolve this is to talk to Hijacking people directly and keep evidence of everything. The way is to click on seller name on amazon.in and use the feature of sending message to them. Write in stictest terms and dont hesitate to send legal notice. To see their address and details, check your test order's bill. It will have seller's name and GST details. You can use that to serve a legal notice and demand claims of sales loss.

Most of the hijackers are timid people and should stop at this, otherwise there's no harm in taking this forward. Also proof of this (screenshots) of this conversation can help you resolve this with seller central faster.

For time-being you can also pause your listing, if they are selling inferior quality product. Or if your product comes with any brand tags or packaging. Just update your first bullet point (Our original product has this "brand name" pasted/printed on box. If you have received a duplicate. Please initiate a return."

Also edit images of product and add how an orginal product should look like. If you dont supply a brand card, get some made in size of visiting cards with your brand name and send with product. This will help customer to differentiate. This should create returns for hijacker and make him suffer some payback loss as well.

I hope with this you issue can be solved.