Comproised network or modem

Someone accessed one of my finances account and wiped out my entire funds. When i called customer service at that finances app. They explained that actuvity happened from same ip address with a nearby location.

how could that happen? Anyway i can prove my case?

Couple days earlier i loged in admin settings and changed ip reset time. Also from time to time i open and close ports for gaming console( recommended by Xfiniyty tech support)