Unhappy with Low quality panel heaters

I bought 4 panel heaters for my home in May 2015.I used it till mid July 2014 and packed it away. This year I took out the same heaters and started using them from June and after a week of use,slight cracks started on 2 of the panel heaters. I have a travel job so not able to always run around to sort or stand in long lines all day.I left the slight cracks and see that it got bigger to the point of cracking and becoming a fire risk to me and my family.These panel heaters have guarantees and I want to exchange two of them for non defective panel heaters.Should I just take it to customer care or what should I do.It is still winter and now we are two heaters short in a very cold house. please help resolve urgently.***