Hello Tris, it does sound like seed infected with virus, you could complain to the supplier but there is no remedy now.
Aphids spread virus too so I hope it does not get into your other, healthy plants, but they may have done enough growing now.
Ironically we are encouraged not to save our own potato seed for more than two crops, because of the risk of virus, but this year my third-year Charlotte is healthy, and I had one of ten bought Charlotte do as you describe, dying off early!
