Being billed for a contract I cancelled

I received a debit order this morning for a contract I cancelled well in advance. I don't see why I am being billed for something that should of been cancelled.<br> <br> Data, calls and sms have been stooped since the period of termination final debit went off yet I'm still being billed. This is ridiculous.<br> <br> I'm resorting to all social media sites until this matter gets resolved.