Tech Mahindra — HR department

Address:

Malad West tech Mahindra

So, I applied for uk retention web chat process on 14th July 2022, and before proceeding for an interview. I confirmed with the HR about in-hand salary package which I will get for the same process.
I cleared all the rounds of an interview, and I received my offer letter on Saturday with different salary package.
Also, as I already confirmed about in-hand salary with hr department before an interview so that's why I refused other Organisations offers.
And now I can't go to any organisation as I already refused there offers and I asked tech Mahindra HR department about joining with them same offer letter but they told me that I am in cooling period now so can't join for next 3 months.

What should I do now?