Regarding Seniority list.

Dear Sir, There was an advertisement for a particular post on direct or deputation mode in a state run institutions. I was applying for same and also got the call letter to attend the interview. In interview, I was declared successful and offer letter was sent to me. In the offer letter, it has been mentioned that, you will be appointed on contract basis for a period of one year. It was also mentioned that, "AFTER ONE YEAR, YOUR PERFORMANCE WILL BE REVIEWED FOR REGULAR APPOINTMENT" . Accordingly I joined on 16th March,2010. After one year of service (27th April, 2011), I got the letter from the authority to attend the interview for regularization of my job. Accordingly I faced the board and my job was also regularized. I got the offer letter in which it was clearly mentioned that, you will be for a probation of 2 years and your contractual appointment will be also calculated towards probation period. That means by the time, I have been regularized, already completed 1 Year & 1 month of my service. In next 11 months (March, 2012), my probation was finished. In probation conformation letter, it was also mentioned that March, 2010 was my date of joining. But now I found that, the authority was not calculating March, 2010 for seniority list. According to them April, 2011 will be your date of joining for seniority list. Kindly guide me.