Don't understand. The value of what goes up? The plan they want to upgrade to is suddenly more expensive? Did they use a coupon to discount their previous purchase? Is prorating enable so it can prorate remaining value?

Are you applying tax? That seams like the only way it'd actually increase.

What would the price be of the 149 and 199 plans with tax added to them? It's supposed to take their final totalizers so any tax or static promotions applied are taken into consideration. It then has to determine how much value the amount of time they used is worth and subtract that. So it'd be something like the below.

( 199 + tax ) - ( ( 149 + tax ) - ( time value ) )

Most likely what's happening is they are saving money, but it's mostly on the tax since 2 days of a 149 plan is very little value depending on plan duration. For example if it's a 1 year plan then 1 day is only worth roughly 40 cents.. so at 2 days they're roughly at 148.20 of value. You subtract that from 199 and you're at 50.8. Factor in tax and it'll easily hit 51.17.