Poor service

I've bought a Polaroid portable speaker box from Zasttra.com, that was on the 1st of 2nd March, it's now the 19th of March 2018. I've been communicating with the agents via email and telephone and they keep on telling me that they've been trying to get hold of the seller without success and this is not this first time that they've been having problems with this specific seller. Who's to say that the problem is really lying with the seller and not with Zasttra.com themselves? They've also promised me to refund me if they don't get hold of the seller but why can't they just discontinue the service of that specific seller? They are aware of the problems and still they make use of them. Unfortunately they didn't wanted to give me the seller's/company name.