Piece of rubber in can of corn

We bought a can of can of whole kernal corn at Checkers in Knysna. After opening it we found a big piece of yellow rubber inside the can. We contacted Mark at customer services from headoffice in the WesternCape. We send him a photo of what it looks like and he apologized and promised to send us gift vouchers. Nothing happened. We've contacted him numerous times amd nothing happened. We contacted head office again and spoke to Wendy at customer services. She promised to sort out the matter amd again nothing happened. It has been two months. Please can anybody help us because its unfair to pay for a product and finding rubber inside. Please can someone help!!!!