That does sound very painful and agreed it's a bad way to treat a customer. BUT the one part I'm confused on: for January - April of 2021, were you actually no

That does sound very painful and agreed it's a bad way to treat a customer. BUT the one part I'm confused on: for January - April of 2021, were you actually not billed $4k each month? If you weren't billed for 4 months, wouldn't you have noticed that when you look at your finances each month? Note: I'm assuming $4k will be one of your larger monthly expenses as a non-VC startup. And even if $4k/mo isn't a huge expense, making sure it's paid is in the critical path of an essential service you have. Now, I'm not saying that a small (small as in # of employees) startup must verify that each vendor is charging them the correct amount each and every month, but if you had previous pain with them, adding a monthly TODO seems like a good idea to protect your business.