Electron scattering off an Anderson impurity immersed in the bulk of a 3D topological insulator is studied in the strong coupling regime, where the temperature $T$ is lower than the Kondo temperature $T_K$. The system displays either a self-screened Kondo effect, or a Kondo effect with SO(3) or SO(4) dynamical symmetries. Low temperature Kondo scattering for systems with SO(3) symmetry displays the behavior of a singular Fermi liquid, an elusive property that so far has been observed only in tunneling experiments. This is demonstrated through the singular behavior as $T to 0$ of the specific heat, magnetic susceptibility and impurity resistivity, that are calculated using well known (slightly adapted) conformal field theory techniques. Quite generally, the low temperature dependence of some of these observables displays a remarkable distinction between the SO(n=3,4) Kondo effect, compared with the standard SU(2) one.
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