Thanks for reaching out to us MarkYS1963, and a very warm welcome to our Community Forums!
Sorry to hear of the charge for the new deal coming into play prior to the ending of the contract.
We would need to advise that as we bill in advance you would be expected to make a payment for the bill of a higher amount, before then being refunded for the dates that are charged at a higher rate.
Once the reduced bill has been received and paid, or the credit on that bill has been spent, the bills would then be expected to settle at their agreed rate.
We would always advise customers to contact our team approximately 30 days before the end of their deal to ensure that a new deal or potential cancellation can be agreed before the non-discounted priced comes into effect.
Thanks,
David_Bn