Business::ISP::Billing points to https://metacpan.org/about/missing_modules which explains :)
Missing module ? - why can I not find a specific module?
Is it in the index?
MetaCPAN uses the PAUSE generated 02packages.details.txt file. If it's not in there, then the module author will need to fix this. (Authors are usually emailed about this when they upload a distribution).
I can see XXX on search.cpan.org but not on MetaCPAN
search.cpan.org has evolved to support edge cases or have exceptions but as the code is not public we are unable to tell you what they are doing.
You module doesnt seem to be in the index
$ cpanm --showdeps Business::ISP::Billing
! Finding Business::ISP::Billing on cpanmetadb failed.
! Finding Business::ISP::Billing () on mirror http://www.cpan.org fail
! Couldn't find module or a distribution Business::ISP::Billing
Why is your module not indexed by the pause indexer? IIRC its probably related to the version...