Under Reg E when it states to "promptly investigate the oral or written allegation of error", is that referring to opening the claim upon cardholder notification? It is understood that if a dispute form/cardholder letter is received within 10 business days that the case should either be resolved completely, or a provisional credit is given if additional time is needed to investigate. But, when a cardholder does not send in a dispute form/cardholder letter, does the claim have to be touched/worked within the 10 business days or do we have the 45/90 calendar days to investigate the claim?

​OPERATIONS

Reg E, debit card, error resolution​

I believe you answered your own question:

"promptly investigate the oral "

once you are made aware, your investigation clock is ticking.