Extra device payment?

Sorry about the vague title,  but the story is odd..

So, my Xfinity Mobile bill normally auto bills on the 7th of each month. Yesterday morning, I decided to pay that bill early before it auto billed. This obvisioly included our device payments for our two iPhone Xs.

That evening, we deicded to head over to our local Xfinity store and upgraded our lines. However, we opted to pay off our Xs and hang onto them. The issue is that the payment I made earlier that day had not appeared in the system yet (which would have made only 8 remaining payments on both phones) so we had to pay the equivilent of 9 payments to pay off each phone. The rep at the store told us this would be credited back to our account, but we would have to call the 888 number to figure out how (credit to the account, or a credit towards our new device payments). 

So we call, and were told "unfortunately we have no way to refund that money". So we are just out a total of $107.34? That seems bit off to me.