You can not "request a rectified bill."
What you can do (instead) is become familiar with how Upwork works, and what your options are with regards to how to use the Upwork user interface.
re: "I told her I would charge $19. It turned out to be 5500+ words. Upwork required me to time-track."
You misunderstood some basic Upwork concepts.
Upwork DOES NOT require you to time-track.
If you want to charge somebody a FIXED AMOUNT, then you use a FIXED-PRICE contract.
It appears that you MIXED the fixed-price and hourly contract models.
Never mix.
If you wanted to charge $19, you could have set up a fixed-price contract.
ALSO: If you had an hourly contract, you could have billed for some time, and then TURNED OFF the time-tracker. That is NOT the intended use of an hourly contract. But if you HAD actually worked for a little while, and then earned $19 with your hourly billing, and then turned off the time-tracker, nobody would have known about it.
re: "I sent her the finished letter, telling her I am willing to make whatever changes she requires. Upwork based the bill on time tracking and sent her a $19 per hour bill which amounts to some $231"
Okay... Upwork did not actually do that.
You did that.
re: "She has paused the contract, hurling abuses at me and asking for a refund. I have assured her that I only ask for $19 still. Please can the amount be rectified and a bill of $19 sent to her. There has been a misunderstanding. And the woman is being rude and calling me thief and my letter a horrible one. Please guide me what to do?"
This is very simple.
All you need to do is issue a refund.
Sutract 19 from 231. The difference is $212.
In you contract list, click on the "Three Dots" icon next to the contract listing. Click on the "refund" option.
Send the client a $212 refund.
Then write to her:
"Mary: You are right. I made a mistake. I am so new to Upwork that I did not know how to use the tool properly. I have now issued a $212 refund to you. So you only paid $19. You do not need to do anything else. The money will automatically be send back to you."
ALTERNATIVELY:
You have the option of refunding ALL of the money. Then NO TRACE of this job will appear on your public profile page. You could even BLOCK her if you want to, and she would have no way of contacting you any further. And you won't need to worry about anything, because there will be nothing that she can do to you (aside from possibly leaving negative private feedback, which will NOT show up on your public page).
My advice:
Issue a full refund. You won't be paid anything for this work. Then close the contract. AFTER you do that, send a short note:
"Mary: I am sorry about the distress that I caused. I am new to Upwork and did not know how to use it properly. The billing you saw was a mistake on my part. I have issued a complete refund. I closed the contract. You don't need to do anything else. All of the money will be refunded to you automatically."
