Contract end date discrepancy

My data contract is coming to an end and when I phoned to give notice of cancellation, your agent advised that my contract will expire with effect on 31 August-18. Why does the contract end date on my online profile state the contract end date is 1 August-18? This discrepancy will result in me having to pay an additional month's subscription and is clearly different to what is communicated to me.

Another suggestion is to streamline your chain of automated selections when phoning 135 as I had to select numerous options for cancellation for 5 minutes to just end up at an Agent that mentioned I had to phone another number for cancellations. It is inefficient and wastes your customers' time.

Please clarify this discrepancy in the end date of my data contract.