Hi AntRC
Welcome to the Community and thank you for posting.
I am very sorry to hear you have not received your promised Amazon voucher.
Unfortunately, as the deal was not directly via ourselves and through a third party, we would be unable to chase this up from here.
We would recommend contacting the third party directly and advising that you have not yet received the offer. If you have any communications from the company detailing the offer, it would be sending that over to them as well.
I do hope this is resolved quickly for you.
Thanks
Nat