Vuse Kiosk Kennilworth Center

Tried to exchange faulty device purchased with various attempts. Eventually contacted them via email. Got the go ahead for exchange but staff at Vuse Kiosk Kennilworth Center would not exchange the devise. They now have discontinued the device. Been mailing backwards and forwards since August. Now they say device was a promo and I must pay difference for device of my choice. Yet the Vuse pen is cheaper than the device I bought. I want this issue resolved without any additional costs to me. The fact that it was a promo and that they discontinued the device is not my problem. There must be a reason they discontinued that device. So why should I pay a difference fir the faulty device to replace it with a different device that's cheaper. I want this issue resolved now at no additional cost to me. The product was bought for me by my friend Tracey Burger