Is there any advice on pj with buttons I bought some by mistake, I don't believe they are safe, but I've been rejected for the return I believe button could be pulled off and choking hazard

Red Nose does not have specific recommendation about type of clothing baby should (or should not) wear for bed.
How old is your baby?
Are you using a sleeping bag?
Certainly buttons & or studs can become a choking hazard if they were loose, & should be avoided in some circumstances.
To help you identify toys and other objects that can pose choking hazards, the ACCC has a free Choke Check tool, which mimics the size and shape of a child’s throat up to 36 months to show how easily an object can get stuck in an airway and block it.
https://rednose.org.au/article/safeguarding-children-against-potential-choking-hazards

Product Safety Australia develops & monitors all safety standards in Australia.
The main focus for sleepwear is on the flammability of the material.
https://www.productsafety.gov.au/products/babies-kids/kids-clothing

Red Nose has information about baby’s bedding/clothing.
https://rednose.org.au/article/how-to-dress-baby-for-sleep