Need advice on negotiation

Hi guys! I am a full stack .NET developer with 4.10 years of experience. My current CTC is 7.1 LPA, and I have an in-hand offer of 15 LPA (14 fixed).

I am looking for other offers as I am expecting a package that is in line with market standards(20lpa). However, the HRs are questioning and pointing out my current CTC, saying that even though we have a budget, we will still be offering based on your current CTC.

How can I negotiate to shift their focus away from my current CTC and crack 20lpa offer?