Double Charged for Handset Installment

I went to upgrade my phone in June 2017 once my contract has ended (not 2 months before when you can upgrade). My bill so far for July and August 2017 has 2 Handset Installments on the invoice. When I called them to query, they said it was because i did my upgrade 2 months before the contract ended so I am still paying off my old phone. For a minute when they told me that, I thought it made sense. But later on, I realized that this is not correct because i wen to upgrade my phone and change my account into my husbands name in May and they said i cannot change the name until the contract has ended. I did not end up doing my upgrade that day as I wanted to wait until i can change the name. So why am i still being charged for 2 handset installments!?!?!