Hi. Sorry to hear of your troubles with your new fish.
Unlikely Pets at Home will reimburse for loss of fish once its been in your tank.
The deaths coud be down to a number of reasons. So a few question will be asked here, but the first and most important qustion is -
Did you cycle your tank before adding fish?
If you're unsure, have a read of the the Fishless Cycling article -
Cycling Your New Fresh Water Tank: Read This First!
Basically what means making sure your tank and filter is ready to deal with any toxic elements that naturally occurs when you have fish in your tank. Namely amonnia, this is what occurs when fish breathe, waste and rotting plants and debris will produce. This is toxic to livestock in your tank, but this ammonia will turn into nitrite once you have the ammonia types of bacterias to consume then this nitrite will start another colonly of bacteria which will turn this into nitrate, the least toxic of the three elements and fish can deal with a certain amount of nitrate short term.
Nitrate is dealt with by us, the fish aquarist, by doing water changes at least once a week of around 40 - 60 % being the normal practice.
Can you describe any symptoms the fish had just before they died, this can sometimes point to clues. For example, did the fish stay at the surface of water, or low near the gravel/sand, appear to gasp rapidly, gills showing red imflamation, lethargy in swimming, or unsual swimming patterns etc etc
The more details of any symptoms you saw in your fish before they passed you can give, the better.
Ammonia, nitrite and nitrate water test readings would be most useful if you have those. PH and water hardness reading may prove useful too, you can get water hardness numbers from you local water authority online.
if you can add if you used tap safe/dechlorinator, water temp and how long the tank has been running and also if you have live plants in your tank.
Once these questions have been answered, we then can proceed to the next steps or following questions. A lot of questions I know and probably a lot to take on but all this will help you and more importantly help your future tank livestocks.