Letter of intent

Sir, I was a permanent employee on scale in a reputed school. It requires me to give 3 months notice to the current employer to quit. My employer refused transfer so i was on look for better opportunities. I got selected for a job n rolled out for letter of intent not giving me much time to read...I sign on same day without signature of their members.I have signed letter of intent of a reputed school on 5th March 2016 to join as English teacher on 21st march. Consequently without the letter only with the photo of the first page I payed money to old employer and quit the organisation. Upon reporting to the new employer on first day I was offered English and science teaching responsibilities...n 6 periods of teaching instead of 4 periods as agreed orally when interviewed...they didnot tell that every teacher has to take two subjects though mentioned English teacher....n they don't pay scales after probation period also got to know from their senior employee ...no one in their office has scales....I am deceived for a non secure job from a secured scale job...n more they offered me consolidated salary of 22 gross though my demand orally was 22net....now plz advice me could I break my letter of intent n join another job without intimating them anything....or I am legally bound to obey it or got pay any notice amount as it had 1 month notice during probabation.