How is it possible for the QB Customer Service not to know

It is possible because they are not properly trained. 

Let me rephrase that,  "they are poorly trained".

One day I'm speaking to some young lady in god knows where, Peru? 

And there is a rooster kock adoodle doin in the background; "background"

as in her kitchen, literally. 

Another day I'm speaking to another lady somewhere near Peru to try to fix

a Merchant Center processing error (they billed the customer twice) and the solution 

she does on a screen share messes up my AR because now the customer go 2 credits

instead of 1.  

Intuit does NOT care.  They do it as cheaply as possible.