Cash back bonus terms not stipulating that I could only withdraw 5times the Cashback bonus

Casino: Greenspins

Claim ammount: 5000 AUD

i won an amount of 5000$ on a Cashback bonus and tried to withdraw that amount to find out that it was rejected and reduced to 375 $ due to there being a condition that I could only withdraw 5 times the amount of my cash back bonus which I had been given 73$ approximately.. I've never come across this before and a friend of mine got cash back of 50 and withrew $1000