Add a text box and use an IF statement to determine which text appears. In the example below, I'm assuming that PaymentForm is the field where you have stored the type of payment -- credit, check, or no payment.
=iif([PaymentForm]="Payment due","Payment is due to be made, payment can be made by credit....etc","Payment has already been made by " & [PaymentForm])
If you change the above line to include the actual name of your payment form field (and if the payment form is stored as a number and the text is looked up, then change the "payment due" in the above statement to correspond to the number value for "payment due") -- then you can copy and paste that statement into a newly created text box. (Remember label and text box are different.)