php - regexp cyrillic filename not matches -

i take list of files php glob(."*.pdf"). files have cyrillic names. example: ООО «Рога и копыта»

then load company names database , try find them in file names: preg_match("/$firm_name/ui", $file_name, $match);

i have problem: firms if $firm_name visually similar $file_name, preg_match says there no match.

mb_detect_encoding both variables return utf-8.

there problem in file name, or maybe there encoding or something, can not understand, ask help.

upd:

$file_name='ООО «Рога и копыта»'; preg_match("/... .Рога и копыта./ui", $file_name, $match); 

as result, ОО «Рога и копыта», 1 О missing