You would use $9.81$ as your divisor. You correctly computed a tension force of $23.62 N$, and stores would say that a maximum tension of $23.62 N$ would mean that it can carry a maximum mass of $\frac{23.62}{9.81} = 2.4 kg$. It's pretty annoying that that is how "forces" are sometimes measured with kilograms, but as a rule of thumb you should always be using what is more general ($g=9.81 m/s^2$ and it is well known) as opposed to the less general things (you're accleration of $2 m/s^2$ which is specific to your case).
Hope this helps.