This is so common.
Firstly create an email account for "accounts@" and send anything to do with invoices from this account. This makes it looks like you are a bigger company and can separate you when you chase. From this account create an email routine. The day it's due send the first chase, two days later send the second, and so on and so on.
Secondly, make sure that your terms and conditions state your payment terms but that they also state the penalties for late payment. Make sure it is on your invoice and the email that you send to the company.
By law, you are allowed to charge interest on invoices after so many days late. Don't be afraid to charge it and include that in your chase emails.
If you do a lot of work for large companies, the person you work for will not be the person who pays you. Get to know that person and contact them directly when the invoice is late and be known as the person who doesn't accept late payment. Don't be afraid to lose clients as a result of this. Every hour you spend chasing money is an hour you are not growing your business. Chasing payments are costs to a business.
Also, look at your payment terms and see if they can be changed. There is nothing stopping you from changing from 30 days to 14 days. I went, after a lot of pain, from 30 days once the work is done to 14 days, to 14 days once the work was confirmed to now my payment terms are 7 days and payment upfront.
It is a nightmare as a business owner and it is completely unacceptable that big companies continue to pay so late, but don't accept it.
Hope that helps a little bit. Good luck.