BAPI_SALESORDER_CHANGE for Sales Order Item Quantity

I Know this might be a weird issue becuase when it comes to this BAPI our common issue was the fields are not changing or updating.

My issue was i need to update/change the value of the Order quantity in the item level of the SO.

what's happening was the value of the order quantity is changing but not according to the value that i have entered.

The scenario was for example i want ti change the quantity from 10 to 12 instead of the order quantity to be updated to value of 12 it's being added to the previous value which gives a result of 22.

Old Order quantity value = 10

New Order quantity value = 12

Expected quantity result = 12

Actual result quantity result = 22.

It's being added instead of altering the old value.

Please help me regarding this weird issue.

Thank you so much