pathetic service, incorrect billing

I am uphauled with the level of service and lack of customer service. Im due for an upgrade on 2 lines and visited a store in Johannesburg and was assisted by Markos. I wanted 2 Samsung S6 edge devices of which I received 1 Samsung S6 edge and a Samsung S6 so I returned it to the store and they were out of stock, called other stores but no luck so I decided to cancel the upgrade.i then discovered that the numbers were switched and visited your store 6 times and liaising with Markos via email as their phone lines doesn't work.i then called the call centre to lodge a complaint and was advised I will receive feedback within 72 hours which never happened and now I get a bill of R2600 for a device I dont have.so I called the call centre again today and told my query was never worked on.i have no problem returning the device I actually have received and cancelling all the contracts I have.im tired of the pathectic service received and the poor call center agents get all the **** from clients and all they can do is apologise and log a request to back office were all the laid back staff get paid for doing nothing, reputational risk but who cares right, it will be a miracle if you respond.