Secured Credit Card Question

I obtained a secured credit card from wells fargo back in 2005 for an amount of $300. I had a loss in my family and went through a period of depression where I didnt pay my bills and the card eventually got charged off. I wanted to make good on the situation and settle up the debt which at the time the lady on the phone offered me a settlement amount but if I paid the full amount she would remove it off completely. Being young and stupid I didnt get anything in writing at the time and of course I paid the full amount and nothing was removed. It's still on there. My question is since this was a secured card and I paid $300 initally should I be responsible for additional debt? I ended up paying $537 (with fees) but shouldnt it have been more like $237 since thats the entire purpose of getting collateral from me in the event I dont pay? Any help would be greatly apprecited.