Can you check and correct my English ?

We have to inform you about something important.

You will receive it -in a week.

The delivery company told us that it might be charged by  the commishion fee.

In that situation, it is going to be deducted from the amount of the payment.

However they don't know how much it is going to be deducted.

Therefore we made a payment which added extra 10 dollars in the case of it.

If there is the difference about our payment, please adjust the payment from the next payment of our transactions.

Sincerely

Thank you.

We did our payment today.

We have to inform you about something important.

You will receive it within a week. *Within is correct if you mean "a week or less."*

The delivery company told us that a commission fee might be charged.
   *the original sentence above is difficult and needs to be reworded. It's unclear if a fee "might" be charged, or will definitely be charged*

In that situation, it would be deducted from the amount of the payment.

However, they don't know how much it would be deducted.

Therefore we made a payment which added extra 10 dollars just in case.

If there is the a difference with payment, please adjust the payment from the next payment of our transactions.

Sincerely,

Thank you *Usually you will only use one "valediction" at the end of a letter. After "Sincerely," try adding a name or company name beneath.

Ex:

Sincerely,

Brandon