Previously this 5 digit number created lots of havoc to many hp users due to spams that involve with expensive charges per SMS. Some will get charge RM1/text, some will get RM5/text, and each time will get more than 5 texts in a week or a month. To curb this issue, most of the telco, including unifi mobile decide to block 5 digit number. Of course, this will create lots of conveniences. Hence what telco nowadays do is, they will make sure all banking and any company that would send out 5digit SMS are in the whitelist.
So for your case, you can chat with the livechat team and highlight your issue to them, for this example sending 33388 with your reason to send. The team will need to investigate if this 33388 is a legit number to be used to send or not.