Notice Period Deduction

Recently I have resigned and left a company, as per my joining letter terms & condition, I can not buy my notice period and I have to serve three month notice period. below clause mention in my joining letter " YOU MAY TERMINAT YOUR EMPLYMENT WITH THE COMPANY AT ANY TIME GIVING THREE MONTHS NOTICE IN WRITTING, NO PAYMENT IN LIEU OF NOTICE IS ACCEPTED", on my resignation I have requested early relieving with one month notice and my HR was agreed but I was not told or given any letter that they will deduct money and i also not asked because payment clause was not mention in joining letter. I have served one month notice and my relieving day they deducted two months Basic+DA from my full and final settlement and balance is transferred in my account and they asked me to sign the deduction letter but I didn't sign and sent email to my HR for removing this deduction because we don't have any commination regarding this. what is the way to recover my money.