Is the tank filled up to the mark, also take a mirrow and look under the flushing rim and clean out the holes with a coat hanger cut, and bent to fit under the rim.
Many thanks for your prompt reply. As you suggested that the problem may be with the bowl holes, we emptied and dried the tank and bowl, applied duct tape to seal holes, poured in vinegar and waited several hours. Unfortunately this did not solve our problem. But we do appreciate your help.