Cancellation of Contract

Good Day I took a cellphone contract with Buy Mondo Hisense u972, I received the package on 25 August 2017, I opened the package the Sunday 27 August I used it but I noticed the battery goes very fast and I wasn't happy with the Device, I called the customer care explained my situation to the consultant advised she will sms me a reference number up till date I have not received the reference number then I sent an email on 29 August and 30th August to customercare@buymondo advising them I want to cancel the contact I have not received any response ever since and this email I sent within 7 days and according to me and terms you can cancel device and will be liable (•If you open the parcel and use the device, you will be charged a reasonable fee for services used during the cooling off period. This will include any data use, calls made and subscription fees) No-one has made contact with me, I am not happy with this device I want to cancel it I am not going to pay the cost of this device. I called and emailed within 7 days and no1 assisted me.