Can you do a phd in maths at Cambridge university without an honours degree?
The definition of an honour student, honour course, etc. might differ between universities, some universities don't have this concept at all. So your degree from your home university might be enough for Cambridge or not, maybe even a honours degree from your university might not be enough.

Who did you email at Cambridge? You might want to try to contact something like an international office, they might be able to tell you the exact requirements for an international student applying.