Over recovery on handset payments

I have upgraded my contract on 23 March 2017. I’ve signed a contract to pay the phone over 24 months. The first installment for the handset were paid at the end of March 2017. However my bill for this month March 2019 still shows that a payment for the handset will be deducted, which will be the 25 payment deduction for the handset, which is contrary to the contract that I’ve signed. I’ve logged the issue a week ago with your call center but I did not receive any feedback. Can you please investigate the issue and come back to me with feedback on my query.