A business claim to have sent me several emails but they never arrive.

Wise, a currency transfer business, claim to have sent me several emails as part of a two stage verification process. But they never arrive! They will not accept that the problem is at their end, they say it must be my email programme which is Thunderbird. I have searched everywhere but they aren't to be seen. They say to look in my spam folder but Thunderbird doesn't have one - Thunderbird flags up what it thinks is spam, (usually correctly), but still deliver to my Inbox. Has anybody any suggestions as to what I should do? Until I login, I cannot use my account.