Hello Pratibha,
There are various courses you can apply for after b.com but since you got 3rd division and also if you want to pay fees in installment then in my knowledge it will be best for you to do some online certification courses like digital marketing etc. as it will help you a lot to build your career and will also land you up in a good job. Also, the fees for such certification courses are minimal, there is one online AdWords certification course run my google which one can do for free, so make the most of such certifications and accordingly build your CV. (All these are basically related to marketing subjects which you might have read in the 3rd year of b.com)

Doing the above will be very helpful as it is -
Cost effective,
Takes less time,
High in value,
Lands you in a good job.

Hope this helps,
Good Luck!