After 4 days of joining I received offer letter from dream company - what to do?

I was expecting a offer from my dream company but they were delaying it so I joined another company. No after 4 days of joining I received offer letter and asking me to join in another couple of days. I am happy but now I joined another firm with notice period of 3 months.
What should I do?

What do you wanna do? Does your dream company know that you have joined a new company? Think over..

No, they dont know. I was thinking to join another company and leave from my current company. Anyhow I do not need experience letter from my current company as ony 4 days I have worked.
Can they take any action against me? I can not serve notice period and they are not ready to release me early.

Hi.
I have joined xyz company on dated 3rd march 2018 but some personal resaon
i had resign on 14th april 2018 , that time my april 2018 motnhs salary kept on hold , giving me apponitment letter there is mentioned one month notice period , but i had given notice period of 17 days , i want salary month april 2018 17 days .....
Please help and suggection please...