Suggestion regarding this.

I have been working in a compnay for last 7 months. (Sales ) ,Now I am not able to work any more due to declining health issues and less salary. And sales is very pressure job. Today I dropped the resign. And my GM approved the resignation. But HR put the email stating 30 days of notice period that was previously 15 days. And 50k of penality as I am leaving the job before 1 year. I am in no way in situation to get back to that place and work. For more 30days . And I know they will not give me experience letter without it. What should I do any suggestions. I am fresher in the filed. Should I just not serve the notice period .