Not keeping to signed agreement

The above mentioned Education provider claims to be of service to many students for several years. I beg to differ. My daughter started a short secretarial course with them beginning 2014. according to the agreement we signed, the course would last 18 months, but if she worked faster, she will get it done in less time and will therefore be billed accordingly. Stating specifically that should she finish all the required assignments before the end of the estimated time, she will get discount accordingly. Needless to say, this was a challenge to her and she worked hard, handing in her final assignment in middle January 2015. Since then she has not received any feedback on that assignment. Every time we enquired, we were told to send the assignment again, because they did not receive it, lost it, etc. With each submission of the last assignment we, also forwarded the proof of previous submissions of the same assignment. We are standing now on the 3rd month that College SA asked for payment,(according to them) they did not receive the last assignment. My husband contacted them numorus times via e-mails and phone calls. We will take legal action against them if we don't get results