Who is liable for a company debt?

Morning everyone, so this is the scenario- John from Company X engages you to do a job, you do the job, you invoice Company X but then in the meantime, John leaves Company X who are now refusing to pay, claiming that John was responsible. I am sure this scenario is very familiar for many people and until now you probably have never truly understood who is liable in these circumstances. Well the good news is this- Company X will always remain liable, regardless if John or whoever your contact on the job has left. The only way this wouldn’t be the case would be if you did the job for John personally but he would have arranged this with you prior to the job proceeding in that case. Stand your ground guys- Company X may still refuse to pay what they believe is John’s debt, but too bad so sad. If that company have benefited from your work, then they have to pay. Simple. Best practice in this case is to send John an email before you start work simply asking “John who should I make the invoice out to?” Cheers