Hi,
You can refreeze them - but I would make sure only to do it once and keep an eye on it when defrosting to make sure it hasn't spoiled.
The more often it has been frozen (and they can get partially thawed several times in the delivery chain to the shop you bought it from on occasion) the greater the chance it has started to decay and the cell damage from freezing makes it more likely it will split open ( and dear lord you do not want to smell that).
Basically I let my nose be my guide and if in doubt chuck it out.
dr del