Most payment processors can be contacted by email. It is preferable to contact them to the email addresses of their legal or complaint departments. Usually, those departments will confirm the receipt in a few days and will likely issue a substantive response a few weeks later. However, some payment processors are slow responders and may reply with substantial delays or may not reply at all.
Furthermore, some payment processors and/or their subsidiaries do not accept legal letters by email. The reason for doing this likely is to reduce the incoming correspondence, thus reducing administrative burden on their staff members.
If you need to contact a payment processor which does not accept email letters, you can send a legal letter by using an online mailing platform. Such a platform will allow you to send the legal letter, without going to the post office.
In your paper letter, it is recommended to mention your email address and ask the payment processor to reply to that email address. This may facilitate your communication with the payment processor.
