Writeoff Excess Paid To Vendor

Purchases a/c

To Creditor a/c

and 

Creditor a/c

To Bnk a/c

this is what happened. Now you realised you have over payed and need to report it, so adjust the Creditor amount in your software

By Creditor a/c 100

By Excess payment 100

To Bank a/c 200

or simply, 

by excess payment 100

To Creditor 100

Hi Mr. Sabyasachi, long time no see, I think leaving the invoicing system, reducing the Creditor by 100 and since bank already paid 200, writing off 100 will reduce the liabilities (retained earnings) by 100 and Creditor by 100 while assets already reduced by 200.