Problem with upgrade cancellation

On the 6th of January 2021, I requested a cancellation on my upgrade that I did in December 2020. By the 22nd of March 2021, when the new 2 year contract period was supposed to start, my request was still not processed. The accounts department started to bill me for the new contract amount, which included 2 devices and data, even though I have returned the 1 device and was issued an RMA number and I never received the other device. I finally received an sms on the 1st of June 2021 to inform me that the upgrade was cancelled effective immediately. However on the 4th of June 2021, I received my monthly statement showing device and data charges for the full contractual amount for the period 1 June until 30 June 2021. I would like to have my account rectified by removing the following from my statement, device charges from March until June (because I did not have any of the devices in my possession for that time period) and data charges for June.