I have no debt except for one credit card that I pay off every month, and I've been in that state for years, but my credit score won't go past the mid 700s. I

I have no debt except for one credit card that I pay off every month, and I've been in that state for years, but my credit score won't go past the mid 700s. I actually tried prepaying my credit card one month so that my debt to credit ratio would be zero, but that made my score drop. It's called a "thin file", meaning they don't have enough data to tell if I'm a risk.