You've got the 25% discount. They're charging you for 7 months (September-March) but you pay over a 4 month period (October-January). For 12 months they charge over 10 months.
181 \* 4 = 724
724 \* (12/7) = 1241.14
1241.14 \* 1.25 = 1551.42
I feel like that might be the wrong calculation (that would only be a 20% discount) but it lines up reasonably.