Thanks for your question
I assume you are able to reconcile the amounts, as I would expect that you know which tenants are in arrears and mark off the payment they have made to enable you to
1) Establish the amount outstanding still with each tenants arrears
2) Keep the tenants informed of what is still owed at the end of each year.
Do you not keep these sorts of records? Despite the fact that the bank only records them as cash deposits.
If not, then you need to ask the bank to identify each cash payment, where it came from so you can create accurate income records.