Appointment letter with lower CTC than promised - what to do?

I am Pallavi,recently joined in a company 1st of Aug,2015. They 1st provide me a Intent letter instead of Offer letter and offered the CTC 3 lakhs pa. when I asked about my Appointment letter, said you will get it soon. On 5th day of my joining issue Appointment letter with CTC of 2.75 lakhs. When I asked ,u offer 3 lakhs at the time of interview but in AL mentioned 2.75 lakhs pa, why? I get replied, you are getting 2.75 lakhs for 6 months(probation period) and after that you will get 3 lakhs pa and still I'm not getting my offer letter. What I'll do?

when you already got Appt Letter, why do you require Offer letter?
Regarding CTC, we don't know what was agreed between you and the Employer during interview process. hence no comment
pon