How to write a cover letter

[#1]

I have send proposal for around three jobs but none of them contacted me back so what should I do to have them reach me out.

[#2]

Hi Kiran,

Thank you for reaching out and bringing this to our attention. Firstly, please be aware that sharing contact information before a contract has started is against Upwork's Terms of Service and that all communications prior to the contract starting must take place on Upwork. Also, a real client will never ask you to give them money to start working, cash a check for them, work for free, or provide your personal information. 

We also encourage you to let us know if you find anything suspicious has happened by using the Flag as Inappropriate option throughout the platform. You can learn more about user reporting here. In the meantime, you may want to check this help article and this thread for more information on how to stay safe on Upwork.

[#3]

Never share your email, number, skype etc. to clients unless you are hired. You can politely decline such request and inform them about this policy. Some new clients are not aware of this but it's against Upwork TOS. Once you are hired you can share your mode of connection with client for the conversation and contact purposes.