I don't see why you could not get a bad batch. Although I am sure they are usually produced to a high standard, the company has no control over what happens to them once they leave the production line. I would wonder if poor storage may be the culprit. Who knows what happens to them in transit! Did you buy a well known brand? Does it have a use by date on it? Has this expired?
If you buy regularly from the same shop and have not had problems before, I would tell them what has happened and ask them for their views. Ask (politely) what they would be willing to do for you, if anything.