24 MONTH CONTRACT ENDED BUT STILL BEING CHARGED DEVICE SUBSCRIPTION AFTER CONTRACT ENDED.

I upgraded my contract in March 2019... being a 24 month contract for which my last device subscription should have been Feb 2021. Upon receiving my March statement this and me being aware that I should no longer be charged a device subscription noticed that I have been charged a device subscription. Then called the call centre who advises me that my contract ends in May 2021 and you can only get through to the cancellations department and no one can assist you with the query on the account. I printed out all my statements from April 2019 and are as follows with regards to the device subscription April 2019Bill - charged subscription for March(1) and April(2) May 2019 (3) June 2019 (4) July 2019 (5) August 2019 (6) September 2019 (7) October 2019 (8) November 2019 (9) December 2109 (10) January 2020 (11) February 2020 (12) March 2020 (13) April 2020 (14) May 2020 (15) June 2020 (16) July 2020 (17) August 2020 (18) September 2020 (19) October 2020 (20) November 2020 (21) December 2020 (22) January 2021 (23) February 2021 (24) end of contract MARCH 2021 (25) thus far been charged for 25 months and still being told the contract ends in May which is 27 months. HOW DO YOU CHARGE 27 months device subscription on a 24 MONTH CONTRACT... by the way the same thing happened with my sister so for those customer who dont take notice you just keep charging them for extra months until it is queried.