Salary Negotiation

Hi, I am new to all these things, so please suggest something. I am having a CTC of 6 LPA, and started giving interviews. Got one offer of 10 LPA, accepted that offer. Now if I want to counter this offer with other companies how to proceed.

1. if I am getting some interview calls and they are asking me the expected CTC, and I am mentioning a number there then they are like we only give hikes based on your current CTC and that too only 30-40% that's it.
2. and if I am mentioning initially that I am holding an offer of 10 LPA. Then they are saying, if you are already holding an offer then why are you giving more interviews?
3. I don't even want that initially I agreed on 30-40 % hike cleared all the rounds and then at the time of hr discussion, hr is clearly saying we don't have that much budget for this role. Then it is a total waste of time.
4. and if I get another offer of more than what I am having now. Then how to negotiate with the current company offer which I am having as it is a product based company so don't want to loose this opportunity.

What to do please suggest something!!??