The irs child tax credit letter says we got $1,650 but we only got $1375. I checked the amount with my IRS online account and it confirms it. what do I do

Do you mean the website confirms what they reported on the letter, $1,650? In that case, you can request a payment trace from them by calling 800-919-9835 or mailing a Form 3911 for the missing payment. There are most likely to be problems with your payment if you closed the bank account that was receiving direct deposits or if you requested checks.

Since the payment trace is unlikely to be resolved quickly, you can still file using the numbers the IRS reported on Letter 6419. This is likely to get your taxes processed the most quickly, but if they later conclude that the number they reported was not what you received, you may have to amend your return to get the missing amount.

If you mean the website confirms that you only got $1,375 as your records indicate, then you can report that as the amount that you received on your tax return. The IRS website's records are considered more up-to-date than the amount reported to you on Letter 6419.