@sharmeela shankar - Sorry for the inconvenience this must have caused!
Firstly, Azure free trial account is valid for 30 days and you get $200 free. The one you are referring to, may be a different offer type.
As far 12 months free services, not all the services are free. You get 25+ free services for 12 months. More details here - https://azure.microsoft.com/en-in/free/free-account-faq/
About $350 charged on your account, may be due to usage of high intensive Azure services you were charged more. You may want to check the services for which you've been charged $350.
Appreciate if you could share the support request # with us for checking the details of your issue and the prices being charged for the services used.
---------------------------------------------------------------------------------------------------------------
If the response helped, do "Accept Answer" and up-vote it.