Are these sentences grammatically correct?

The accounts department has passed our claim, and the payment was calculated from the date of arrival of the candidate, not the date of course.

As s result of this, an amount of $1000 was overpaid the candidate. The claim was passed after the departure of the candidate, and it was not possible to recover the overpayment. The amount was paid from the temporary source fund and the shortfall of $1000 has been reflected in this fund.

The clecrical error was due to the oversight. In view of the above, I am willing to pay $1000 to recoup the amount in the source fund.