I doubt you learned the material in the courses if you earned a C. You are unlikely to succeed in graduate school without A level knowledge in these subjects.
However, you do not have to repeat the Bachelors. You just need to get admitted to a good undergraduate institution with a graduate math program as an adult student or some other more individual status. Then retake the exact set of courses: 4 math courses per semester should get this done in a year unless the courses are sequential, in which case you need more time.
The reason this needs to be done at a good undergraduate institution is because you are going to be asking for letters of recommendation.
At CUNY we get many students doing this every year, mostly students who are planning graduate school in a field which requires more math than they took when they first got their bachelors but a few who took the coursework a long time ago or didn't do well in it. These are some of our best students and we are happy to recommend them to graduate programs based on their coursewok even though their Bachelors is from another institution.
