What should I do if my salary isn't being credited via GIRO?

Check with your HR why this is so. I'm not sure about your situation but sometimes it is only the first month salary that you will get via cheque due to pro-ration. Most companies should be paying their staff salaries via some form of bank transfer or GIRO instead of cheques or other forms of payment modes. Companies that do via bank transfer and indicate in the bank transfer reference as salary would also satisfy this criteria.

Yes, check with your HR why it isn’t. And see if you can change it.

Your HR should be able to help you