Under the heading Not Quite Ready for Tax Season the IRS is urging people to use the 
information in their online taxpayer accounts for the most up-to-date figures on the amount of the advance Child Tax Credit to include on their tax returns — instead of the numbers stated in the letters it has been sending.
The IRS began hearing questions from reporters the day tax season started on January 24 about why some of the letters the IRS had been sending to taxpayers who had received the monthly Child Tax Credit payments seemed to have incorrect amounts. The IRS believes the inconsistencies are relatively limited and mostly apply to taxpayers who have changed addresses, whose payments were undelivered, or where the direct deposit failed to work, perhaps because they changed bank accounts.
The best answer, as always, is to check your records and bank statements to see exactly what you received. This is another reminder that it is never a good idea to leave the record keeping for your taxes up to a third party, even when that third party is the IRS. W2s, 1099s and other tax documents you receive are not always correct and if you have the records to prove they are wrong you can use those records to make sure you don’t over pay your taxes.