Mark the first question, then very carefully review every little bit of the form, before resubmitting. That they mentioned you not answering the first critical question, does not mean they even looked further at your submission. Review the whole package. Check the instructions for the I-130 to be certain you submitted all the "required" supporting documentation.
Since you are the purchaser of the financial instrument you used for your first payment, the issuer should only charge you the difference for a new one for the increased fee.