Complex counters scenario

Hi team... her we go again... this time we are requiring to build the following scenario:

We need to count the number of annual service calls set for a customer with a 'granted' free amount of calls.

The billing for the customers happen monthly but the call allocation is yearly.

So:

Customer A - Yearly 'free' calls: 10

Billing: Monthly

January: 2 calls(total /year = 2)--> Billing = 0

February: 6 calls (total /year = 8)--> Billing = 0

March: 4 calls (total /year = 12)--> Billing = 2

April: 6 Calls (total /year = 18)--> Billing = 6..... because out of 18, 10 re free and 2 were already billed in March.

Any idea on how to model this scenario using the Usage Type maybe? (Actual per period=Year or Actual by quantity)?