I was shocked to see they added 25 % to my income due to not having taxes taken out until I file. Is this legal. I was told they take 125 x monthly income. It's higher than I can afford.
Not nearly enough information to speculate on answering your question. For starters, you state your location as South Carolina which doesn't allow "private party" garnishment for "consumer" debts. So, I can only assume we are talking about possibly a tax debt, maybe federal student loans, child support, etc. All of which have different rules for how much can be garnished.
But on the face of what you say, if you really aren't having taxes or anything else withheld from your income, then yes, they can garnish more. Most garnishment rules are worded either as a percentage of gross income, or a percentage of income after necessary withholding (fed and state income tax, SS, and medicate).