Most of the time, changes in the amount of payments are related to your income plan, please check your income plan on My pages and check it is correct. It can also be that some of your payments have expired, such as for example, the home allowance stops when lease contracts expire or you move houses and don't let TR know. 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 My pages of TR.