Cannot Cancel my Contract Correctly

I called to give my notice of cancellation today on the 9th April 2015 for my contract expiring on the 31st May 2015.<br> I was then told that my contract will be terminated on the 28 June 2015. When i questioned why if i am giving about 8weeks notice of something expiring on the 31st May will the contract only be terminated on the 28 June? Besides the lady who helped me got very rude when i was asking questions around this. This is completely unacceptable and how can i be billed for an additional month if i am giving more than sufficient notice to terminate at the expiry of my contract. I want this resolved. My contract will be terminated on the 31st May as per my contract with Autopage.