Lots of sellers are requesting the Udaan Seller Support contact number, they have the same line for sellers, buyers you can find it on their official website.
Seller support Contact: 1800 121 0985
Seller support Email ID: help@udaan.com - This is the only support email available now in public
You are likely to receive a response in less than 48 hours on their email.
If you want to know more about the Udaan selling space read the following post.