Ah yes sorry, don't know how I misread that. I agree, it wasn't a one off fare evasion. OP, just wait for the response if you've sent the letter already. Don't stress too much. Have you considered taking legal representation to court?

You got caught in Nov 2018 and it's dragged this long!? - How long did you use the fraudulent card? - Were you paying correctly for your fair before obtaining the fraudulent card? - Can you get a statement from someone of in a position of trust to vouch for your good character? As mentioned, TfL lose a lot of money from oyster scams and they do not take it lightly AT ALL. Lesson for all: please don't dodge fares. You break the law once and that can be a mark you carry for life. Hope all goes well buddy. Don't lose hope.