You have not received the undertaking/affidavit by Email then
Please check it in the SPAM/JUNK Folder of your email, it may be there. If you still do not get it then ...
Your undertaking/affidavit carries a wrong Parent's name.
In both CASES
Apply for the duplicate as under:
If you do not have the reference number, please resubmit the Online Undertaking/Affidavit as many times as you like and rembember to note down the reference number.