you may need to take it to your dealer and have them align primary and secondary. They have a tool for doing this correctly, and involves moving the motor in it's mounts and shimms. Last time I had it done it was like 70 dollars, but it instantly stopped eating belts that I was replacing about once a month.

 

i was out this weekend and i shreded a belt on my 05 800 with only 140 miles on it.we were on an overnight ride and luckily made it to a dealer just in time. 85.00 wow didnt think a belt cost that much.i had a 95 sportsman that i just sold with over 7000 miles and never had to put a belt on it

 

the belts have a lifetime warranty, get your money back unless they charged you for instalation.
There must be a problem if it went that quick, check the alignment (dealer) and use low range when advised to by the manual.
I have over 1100 miles on my 700 without a problem.

 

The dealer I have didn't charge a dime for replacing my belt ar 560 miles, parts or labor. Better check into that.