The correct answer is, they are HOMOTOPIC.
Let us use the substitution method to see.
First, I am substituting Ha with Br. Now, using the CIP rules, first priority goes to Br, and the last priority goes to H. Now the problem arises. How to assign second and third priorities.
This problem is solved using the Zeroth Rule. "If two groups are completely equal except for their spatial arrangement, assign priority to the group that is pointing towards you".
Thus, I have numbered the groups, and found out that the configuration is 'S' (anticlockwise).
Remember to view the molecule in such a way that the least priority group is pointing away from you.
(I have included the fiscer projection too, for ease of understanding)
Now, let's replace Hb with Br, and assign the configuration as earlier. Note that the Zeroth rule is used here also. Again, the configuration is 'S'.
Thus, they are in the same chemical environment, and are HOMOTOPIC.
In an ALTERNATE METHOD, there are two Chlorine atoms adjacent to Ha, one cis to Ha, and the other trans.
Likewise, Hb also has two adjacent Cl atoms, one cis and another trans. Also, there is no other element of chirality on the molecule.
ie, it doesn't have a point, axis or plane of chirality. Therefore they are chemically similar, and are HOMOTOPIC.
However, it's better to use the first method, since it is the best one.
NOTE: I would be happy if anyone can suggest a more verbally accurate statement of the 'Zeroth law'. ( If mine seems flawed)
I have confirmed the answer from my professor, but I have written the law in my own words.