Most of the time, changes in the amount of payments are related to your income plan, please check your income plan at My Pages Ísland.is and see if it is correct. It can also be that some of your payments have expired, such as your home allowance stops when your legal domicile is moved without notifying TR or someone else registers at your legal domicile. It is best to see if all payments are included in the payment plan for the year or on the payment confirmations that come every month on the My pages of TR and there under My documents.