Translation:I chose to no longer come to the office on Mondays.
This may be a fair, if very cumbersome translation. If we were at the office then we would be more likely to say "I chose not to come to the office anymore on Mondays." if we were speaking outside the office we would say "I chose not to go to the office anymore on Mondays".
On Mondays, synonymous with every Monday, has the definite article le. For on Monday, when referring to the particular Monday in the future or in the past closet to the present time, lundi will be be used without the article. You might want to chech back whether the example without le was for on Monday or on Mondays.