If I do not collect the sales tax or collect an incorrect amount, who is responsible for paying the correct sales tax to the Comptroller’s office?

You are responsible for collecting VAT from the customer even if you have not received it in the original, So they are not registered when they are discovered by the tax department, and they are held accountable for the tax and the fines resulting from them. They did not collect any amount

If you are responsible for that collection and you have received the correct training about it, you and your manager should pay for that , unless you can persuade the original tax payer to proceed.

If not, your company should proceed, as they have not informed or trained you.

The best way to avoid is to bring all necessary items in the contract prior to any procedure and have it countersigned by the customer. In this case even if you have forgot to proceed with the right procedurer, the customer is responsible. 

Dear Mam,

The Assasse (the Tax collected person/company) has to be pay the correct amount of TAX to the Government while Filing the VAT return

It all depends how much business you are showing all irregularities will be corrected by a charter accountant before filing the tax and mostly at that time the company has to pay