If the economic impact payment letter amount does not match the actual amount deposited into my account... which total should I use?

It depends.   What is your filing status, are you single, married filing joint, or married filing separate?   What was your filing status in 2020?   Do you have dependents?

If the amount on the letter is less than the amount you received in your bank account, my recommendation is to use the amount in your bank account.  (Make sure the amount you are seeing in your bank account is for the third stimulus payment.  

If you are married filing joint the amount received was split between the taxpayer and spouse on your 2020 tax return.   If you are single or head of household, did you claim dependents in 2020 and not claiming them in 2021.   

If there is a reasonable explanation why there is a difference between the letter and the amount deposited, enter the amount in the letter.  To give you a more exact answer I would need to know what we are talking about as to the reason why the two do not agree.    

One question, do either of the amounts match what your return is saying you should have received.  If one of the amounts does, I would use that amount.  

If you are not able to determine which amount to claim from my response above, then respond with more details and we could give a more exact explanation.