I can't help troubleshoot this device, but your other question about batteries makes me wonder if they are authentic and capable of powering the mod, did you purchase them from the vape shop? It can be fairly typical of vape shops to sell "branded" batteries that really are other cells that were rejects from more reputable suppliers.
I don't understand why the store you bought it from is not being more helpful... If you are genuinely having problems they should help you sort it out, and either repair or replace. I know it's difficult at times, but I would be informing the shop that if they don't assist you with the device (I'm assuming you were using it correctly and haven't done anything to void the warranty) that you will be having that charge removed from via your bank or credit card's fraud system. Whether you return the device to them is up to you. Is this a brick and mortar or online store? IF B&M and they're few and far between in YOUR location, you may want to be a bit more tactful about it... If they're an online vendor and they won't assist you, it is well within your rights to have them "honor" the warranty whether they so desire or not, by asking for a chargeback after explaining you received a device that is non-working, and the vendor will not assist you in warrantying it.
It's not the most uncommon request ever made to a bank, though I like to hope that more vendors are standing behind the products they are selling. After all, it's not the vendor that will be doing the "funding" of the warranty, it would be the manufacturer.... Unless you purchased it off ebay for example, in which case things may get trickier.... Good luck. I don't know the mod, so I can't really comment as to what may be causing the problems.
Anna