Another bag of rotten potatoes

I purchased a bag of potatoes last week, then 2 days ago I found many rotten potatoes in the bag, whilst the expiry date on the bag was only 14/05/2018 so I took it back without a slip and they kindly exchanged it for me. Today, I found another 6 rotten potatoes in the new bag! I stay on a farm, therefore I don't have the time and money to waste on having to go and exchange in store. I always used to buy my groceries there, but this potato thing is highly upsetting.