How to prevent user from adding a second pay period method type when two payment types are available

Summary:

We want to prevent user from adding multiple payment methods when two payment types are available. 

Content (please ensure you mask any confidential information):

We have two PPM types - check and direct deposit. We want to give users the option to choose only one. We do not want them to have direct deposits and check. Seeded functionality available does not prevent a user from creating a second PPM's if two payment types are available. Need to know how others were able to get around this and prevent users from creating a second payment method.

We do not limit the number of direct deposit accounts. What is the best practice or what has worked to prevent users having both PPM?