LTA

I am an employee of a BPO. Under my company policy, I can claim LTA of 20k per year and can also carry forward for the next year. Now if in a four year period I claim 2 year's LTA at once i.e. 40k in say 2nd year and 40k in 4th year, Can I claim whole 40k for for IT exemption? that way i will claim LTA for 2 times in a period of 4 year.

My company says I can claim tax benefit on 20k only and not the carry forward amount, even though I spend 40k in the single travel... Please guide me...