If you believe you were duped and want your money back your first option is to ask nicely. When that doesn't work you then write a firm demand letter that indicates your intent to sue if your demand is not met. Then, when they completely disregard your demand, you go to small claims court and explain it to a judge, thoroughly indicating how the problem came to be and how you attempted to resolve it on your own. The judge will decide wether or not you are entitled to the refund, and then you can attempt to collect whatever you might be awarded.
It sounds like you are at the demand stage. Let them know you are serious. Clearly, but politely, indicate in writing why you believe you are entitled to the refund and inform them you will take the matter to court if they don't comply within a reasonable time... maybe 7-10 days.
For $1400 this is not something you will want to hire an attorney for. There is no reason why you can not handle this on your own and proceed through small claims court. Small claims judges do not expect you to be legal geniuses.