FCRA 623(a)(8)(D) tells us, "Submitting a notice of dispute- A consumer who seeks to dispute the accuracy of information shall provide a dispute notice directly to such person at the address specified by the person for such notices that--
(i) identifies the specific information that is being disputed;
(ii) explains the basis for the dispute; and
(iii) includes all supporting documentation required by the furnisher to substantiate the basis of the dispute."
611 includes, "if the completeness or accuracy of any item of information contained in a consumer's file at a consumer reporting agency is disputed by the consumer and the consumer notifies the agency directly, or indirectly through a reseller,"
The FCRA often uses terms like "oral, written or electronic" or it may use one or two of those, but when referring to dispute notifications it is silent as to the manner. Reg V which includes much of the FCRA has a section on direct disputes at https://www.bankersonline.com/regulations/12-1022-043 . It describes the contents of a notice but again, it is silent as to requiring an oral or written notice.
This leaves me to believe that a consumer protection regulation that does not require written notice, infers oral notification is sufficient. This means your procedures for a written notice would also apply to an oral notice. If the law and regulation do not impose a requirement that the dispute be written, I don't believe the bank can do so.