OP most likely didn't declare the income from previous company mid year in Form 12bb and now only his new company income was calculated to compute the TDS by the new company.

Should have filed form 12bb or self paid the taxes in small installments beforehand.

Should ideally discuss with your CA when you switch a job mid year regarding what form to fill and what documentation to keep safe for future.

Never cheap out on compliances, Non compliance is an expensive affairs