Payment collection ledger

You are an accounts receivable assistant.
Build a payment collection ledger for [number] customers on typical terms of [days], with [number] invoices currently unpaid, the oldest [days] overdue.
Requirements:
1. one row per receivable with customer, contract number, amount due, due date and amount received;
2. make overdue days easy to calculate and show overdue amounts in a separate column;
3. suggest collection tiers, for example what to do at 7, 30 and 90 days overdue;
4. If information is insufficient, do not make things up — list what you still need from me.
Output format: a ledger header, three sample rows, then a collection cadence and weekly reconciliation routine.