Didnt inform me dates to cancel contract for a 3rd month after my contract expired

I phoned 2 months back to cancel my contract. The agent told me that i have to wait to months and call ones my debit order goes off ones it went off my account. I was following their procedures and phoned after the 20th no one told me that i had to phone the 18th. The retention lady told me i have to pay this payment if i want to cancel my contract. Is the purpose of the retention department to fustrate and prolong contracts. I wish their was a 0 he because if i did what i was suppose to do why dont they do what they suppose to do. I am livid and my recordings can be listene to. Nowhere they advise me of such a thing. Cell was always tops with service but i will never use them again