Silicon Solar - SiliconSolar.com Sold me item they did not have and wont refund all money. ithaca, New York

I've ordered a solar system with a tank to hold domestic water and that has an electric back-up element. Tee tank i got has no heat element  does not hold domestic water and for that can not be pressurize. After for month i got them to agree to refund all my money and to take back the tank plus components. I shipped back the tank and after 2 months of fighting they refunded 2/3 of the amount. Now i am fighting for the remainder and they said that they will not refund shipping even though they agreed to that in writing. This company has very unethical business practices and needs to be stopped. Further more i want all my money refunded as agreed prior.