I have made the following simulation with the circuit you can see below:

I'm asked to find the cut-off frequency for this filter. From the simulation, it looks like it \$f_c = 500 \text{Hz}\$ or somewhere around there.

However, if I use the formula for cut-off frequency I get something totally different.

\$f_c=\frac{R}{2\pi L}=\frac{500 \Omega}{2\pi \cdot 10 \text{mH}}=7960 \text{Hz}\$

Am I using the correct formula, or is my interpretation of the simulation wrong?

I hope someone can help me.