If you have to deal with a Sky call centre, it can be tricky to speak to someone who is authority and can make decisions. They, like many companies, have layers of low level staff who are there to field standard enquiries with standard answers.
To escalate to a supervisor, or better, a manager, can be tricky so you have to be persistent and forceful in a gentle and polite way.
Ask the call centre person for the name of their supervisor and the supervisors manager and contact details. Ask to be put through to them, even if you have to wait on hold for a while - supervisors always seem to "be busy".
When you do get to speak to a supervisor, ask them for their managers name and say that you will escalate the problem to them if the supervisor doesn't help you to your satisfaction. Do not take no for an answer.
Take the time to find out about their organisational structure and work your way though it layer by layer until you get the problem sorted. Always being polite, always being diplomatic but persistent.
I have used these tactics to good effect with call centres and I have resolved some difficult issues this way. I even appeared on a BBC consumer programme last year when they heard about one epic battle I had with a BT call centre.
Good luck