Aging formula

Here is the problem: I work for a property mgmt company and our delinquent policy is stated as follow:

$150.00 balance carrying > 11 Days = Letter 1 (reminding you are late)

$150 balance carrying > 42 Days = Letter 2 (sending second notice)

$150 balance carrying > 52 Days = Letter 3 (sending to court)

Let’s say, Fees due on Jan. 1st. Jan. 10th grace period ends. Jan 11- John receive L1.
No payment received from him as of Feb. 10th. So he is 2 months behind. He gets an L2. Still no payment received from him by Feb. 21st. On Feb. 22nd he receives L3. However, if he pays on Jan. 31st, he will catch up for Jan. Then if he is late again on Feb, he will receive a L1 on Feb. 11th. Sooner the balance reaches the threshold amount; the cycle starts from the beginning.

I can run the report from software at any given date and see the delinquent folks and the total amount they owe as of that day. I can even filter by delinquent amount and run reports for folks whose balance is > 150.00. The challenge is when it comes to assign the appropriate letter. Any help would be highly appreciated. Thanks.