What should one do if neither the original creditor nor the collection agency mails monthly statements as to what is owed?

Once a debt goes into default, the entire balance is due and payable upon demand. This contingency is part of every contract which establishes debt. You lose many rights once you default, including the right to "make payments". If a creditor or collection agency agrees to take payments, they do so at their own discretion. Since such an arrangement would be case-specific, no monthly statements are ever sent. You may contact either the OC or CA to find out what the balance is. Then make arrangements to pay in either part or in full. Either way, you will be expected to keep those arrangements.