Rejected return to swap for the right size

My wife purchased some sandals yesterday. I tried them home they were small so l decided to return and swap them today (next day) for the right size. Customer service argued l used them and washed them. How could l do such a thing. I get excellent service from Truworths which is just opposite, problem they were closed so my wife was forced to buy from Woolworths. I will NEVER buy from Woolworths again and wouldn't recommend anyone to.