We are using Contracts (P1720/P1721). Having problem with contract Billing

The contract is created for 1 year, say Oct 14, 2020 to Oct 13, 2021.

The Billing is to be done annually for $3000.

The contract dates are fine. Bill from and Bill through dates are getting updated as 10/14/20 to 10/31/21 (Period end date ). Due to this, $3000 is is being spread into 386 days.

When we run billing, it bills 10/14/20 to 9/30/21. and then balance is billed in the next year.

Expected outcome:

Billing of October 14 to October 31.. 1 bill --> 140 ( prorated amount)

Billing of November 20 to Sept 21 as may be 11 bills of 250

Billing of October 1,2021 to October 13,2021 --> 110 ( prorated amount )

Can anyone please help if you have seen this problem.