You can dial 18004252440 for Customer service of Post Office Savings bank like for Lost or Stolen Cards, you can call there Toll Free Number 1800-425-2440.
If you reported the ATM or Debit Card lost or stolen, and in case you found it do not use it again. You can apply for the reissuance of the card.
For any queries realted to Post Office Savings Bank Account you can also email them at postatm@indiapost.gov.in