This happened to me when the local credit union, TechCU, overhauled their web interface and app. I called their help line and stumped them for a while. I finally figured out their interface allowed me to use a period in my password and confirmation field and accepted them but somehow their login process did not. To their credit the characters they listed as allowable did not list period which I did not read carefully and just skimmed the first time I saw it.
This year I don't even get to the point of making a password. It's possible something about my attempt 10 years ago has polluted my phone number. So it goes.
Notice, too, that my story is about the utter lack of support like in OP.
