Is the '°' wrong in a degree centigrade mark?
For the International System of Units, the units of measurements are defined by the SI brochure. For the degree, unit of plane angle, and the degree Celsius, unit of Celsius temperature, the SI brochure at p. 133 and at p. 149 uses a circle and not a zero.
However, at table 8, the circle is rendered with an &quot;o&quot; (probably they didn't have the circle in that font). In any case, no zero.
You can refer your professor to that document. Further, if you're using LaTeX, you can use the siunitx package and write the angles with the command \ang and Celsius temperatures with the command \SI{23}{\celsius} (example with 23 °C). From the package documentation, you can see that also in this case the degree symbol is a circle.
If they still insist, let it go.