Hi Sanjay,
Please check the contract number on catalog item or on source of supply tab field "contract" of the shopping cart item. Once you get the contract number, login as strategic purchaser to access contract management in SRM.
Contract management has active queries the way it has for SC/POs. You can search for the contract and on header data you should see the validity dates (from and to). You need to extend "To" date for the contract.
Regards,
Ravi Pachauri