I'd rather re-write the message as a whole than try to correct lots of individual errors that are in your own draft. Here's roughly what I'd say:
"Further to my previous emails (which have gone unanswered) I note that I have still not received the refund of my health insurance premium (€231.00), which was previously agreed by your company.
I acknowledge your initial attempt to make such a payment but that did not go through due to the payee name quoted by your company not matching the account details that I provided. I repeat my request for the payment to be made to MY SISTER'S ACCOUNT and NOT to my own account. (i.e. please ensure that MY SISTER'S NAME is quoted as being the payee).
The account details are as follows:
Name of payee: [Your sister's name, in CAPITALS]
Bank: [Name of bank]
SWIFT: [Bank's SWIFT code]
IBAN: [The IBAN for your sister's account]
Sort Code: [The sort code for your sister's account]
Account Number: [Your sister's account number]
I need this money urgently and I would therefore be most grateful if you could process this transaction as soon as possible.
Regards . . . "