"A foreign importer signed a contract with an import and export company in China for 500 metric tons of wheat. The contract stipulated that the L/C should be established before January 20th, 2009 and the shipment should be before February 5th. On January 28th, the importer opened the L/C which was valid until February 10th. It became difficult for the seller to ship on time, so the seller asked the buyer to extend the time of shipment to February 17th and the validity of L/C to February 20th respectively. The buyer agreed but didn't inform the opening bank. The goods were shipped on board on February 17th and the seller presented the shipping documents to the bank for negotiation, the bank refused.

Questions: Does the bank have the right to refuse the payment? Why? How should the seller deal with the problem?"