Dry and crispy leaves suggests under watering. The lack of growth is possibly down to not repotting them - are they still in the original plugs? They need fresh soil and larger pots/put outside to grow.

Yes I put them in larger pots as soon as they arrived and they are well watered, the soil is always moist.

Could they have been frosted.I would dig one up and inspect the roots. Did you tease the roots out at all before planting them. Maybe they dried out somewhere else before you got them and that allowed the roots to die even though they looked healthy when you potted them on. Most companies will help if you alert them to the problem. Did you use multipurpose compost? How big were they? Did you get care instructions with them and did you follow that?