Lost old email address, can't get sign-up bonus

I recently lost access to my old email address, and I have had to change everything over to a new one. I was able to do this with my iD Mobile account itself fairly easily, but I am not sure if I will be able to get my sign-up bonus. I only joined iD because, with the sign-up bonus factored in to the cost, it was better value than my previous mobile provider. However, I have not received this bonus - a £45 Amazon voucher, which would bring the “real” cost of my 12m plan down from £8/m to £4.25/m. I’m not sure how this bonus will be given to me, but I remember being told that I should receive it within a couple of months of starting my plan. However, it might have been sent to my old, inaccessible email address. I’m also not sure if the bonus will be provided by iD themselves or by some other third party. Can anyone help?