Could you teach some knowledge of law on this issue?

A big company has a policy that for the complaint with its service from customers, the company only accepts phone call (that is, refuse communications in e-mails and regular letters).

Personally think that such a policy is obvious discrimination to a specific group who has limited English level. The people in this group got bad service from this company, it is not possible for them to do complaint.

I feel confused for the law on this issue. The company openly says this policy. That means that it is legal. But is it really legal?

Could Old Cat and/or any experts help to clarify it? Thanks.