How do you know you were supposed to get a letter? Did you talk to the IRS by phone, or is that a message shown on the IRS "Where's My Refund" page?
https://www.irs.gov/wheres-my-refund
Do you have an IRS online account? If so, you can look there to see if there is a copy of any letter. But it's not foolproof since they don't post all types of letters there.
"person has not been leaving my mail in my mailbox"
That's not good. You need to go talk to your local Postmaster and complain about that. What has the person been doing instead with your mail?
You can speak to the IRS. If you get a triage robot, try just saying "speak to account representative" (may have to say it more than once).
IRS: 800-829-1040 (7AM-7 PM local time) Monday-Friday
Or if you can't get good info from the IRS, you can see if the IRS Taxpayer Advocate Service will help you. They are especially prone to help if you are having an economic hardship or have delays with lack of info from the IRS.
https://www.irs.gov/advocate/who-may-use-the-taxpayer-advocate-service
https://www.irs.gov/taxpayer-advocate