Tickets will be sent to each individual assigned customer, first thing to check is that all assigned accounts hold the same email address.
If the email address on all accounts is the same, it may be possible that the emails have grouped. Email grouping tends to happen on accounts using Gmail or BTinternet.
Next to the sender you will see a number which indicates how many emails are in the email chain, as shown below.
Once clicked onto the email at the bottom you will see 3 dots, as circled below. Clicking the 3 dots will expand the email displaying the other ticket and download links.
If you still cannot find the ticket, please send a request.