tmart.com its a website ripped me off Internet

i ordered a keyboard tablet case from tmart.com, but the cord to connect the tablet to the keyboard was not the correct size.  i went back and forth in several emails with them about this.  i browsed their site again looking for the size and color i wanted, which they did not have.

so i returned the case via fed ex, which cost me 8.00 to return a 15.00 case.  within 30 days of receiving it.  since then i have sent many emails to them requesting a refund under the 90 day money back guarantee they have posted on their site.  they have not responded to any of my emails that were requesting a refund.  it infuriates me that a company can blatantly ignore your repeated request for a refund.  its not about the money, its the principal now.  the case was returned back in june and i still have not received my money back or even a response from them regarding this.