Still no feedback on ending my contract!!!!!

I have complained 3 times, called 3 times and e-mailed 3 times to your useless company. My tablet contract ended on the 17 May 2015 and I called on the 18 May 2015 to change it to prepaid. I was told I would get a call and I have heard nothing since. I will be returning every debit you take from me as I work for a bank until you sort your useless service out. I want my tablet contract changed to pre-paid immediately. I will not wait until your strike is over and then have to spend weeks trying to get you to refund me.