Guaranteed surrender value in life insurance policy

I have one Endowment policy in LICI in my name, table- 14, date of proposal - 7/12/2012 of sum insured 15 lacs, 27 yrs.term; 3 yrs. Passed. Now I want to surrender. I had paid Rs. 28000/- per premium in half yearly mode , so I paid 6 premiums till date I.e I paid Rs. 168,000/- till date. The vested bonus added is Rs 140,000/-. The 'Guaranteed surrender value ' clause in the policy bond shows- " The minimum surrender value mentioned premiums paid excluding the premium for the 1st yr and all extra premium &/or additional premium for accident benefits. The cash value of any existing vested bonus additions will also be allowed". The accident benefit premium I had to pay was Rs. 1500/- only. The surrender value LICI now showing is Rs 72000/- only. They are using some formula by multiplication by surrender Value factor. It is not written in the terms and conditions in the bond paper. I informed them that I am to be paid Rs. (168,000+140,000)-{(28,000×2)+(1,500×6)}= 243,000/- and not Rs. 72000/-. But they are refusing. May I challenge LIC's such decision? Pls. Help.