Even after disabling the IdP or deleting the IdP record, users are redirected to the IdP URL.
Auto redirect and default IdP may or may not be set.
Release or Environment
Check SPEntryPage (https://<instance>.service-now.com/nav_to.do?uri=sys_script_include.do?sys_id=3647c37253221200b0b0547cedc587fd) for customisations. Any hardcoded redirect statements may send users to an old IdP.
Revert SPEntryPage to OOTB or modify the redirections.