cart checkout is not calculating correct weight

[psco]

Hope this is the place to add this. 

My site is selling products which are dropshiped from overseas, just one collection. I set up shipping the rates they gave me to use. example 0-1 Kg 9.80 : 1 to 2 Kg 14.90 ; 2 to 3 16.90 etc. Added the specified collection to the shipping rates.

I get and a couple of orders and the weight comes in from the customer at the lowest.  0-1 kg. 9.80 it should of been 16.90. 

I tried a sample order and seem the problem is instead of charge by the total weight it is letting the customer choose what they want to pay on the chart i set up?

How can I fix this asap. I don't know how to start on this problem.

Ron