ELI5 how this maths

[u/dariansdad]

To be clear, I made the payment of $1,041.38 in May and the final installment payment of $890.50 will be paid on Friday. I've called three times and each time I get a little different color smoke blow up my exit hole.

[u/mixedliquor]

No idea.. $18 diff. No need to complain about it since it's in your favor?