I got round a similar issue by a nifty trick, that you may be able to apply.
It involves firstly creating a CLONE of your shipping module. (There are posts of the forum about cloning shipping modules).
Then, secondly, adding a couple of simple CONDITIONAL statements to the php in the module files.
If you like, I can send you two shipping modules called:-
zonetable
and
zonetabletwo
that are basically configured to achieve this.
What happen is this...
If a consignment shipping weight is LESS than a certain value, then zonetable kicks in and zonetabletwo is hidden from view.
If a consignment shipping weight is MORE than a certain value, then zonetabletwo kicks in and zonetable is hidden from view.
So, if a shopper's cart total weight is UNDER 150kg, then zonetable will kick in (and you'll configure this to suit your freeshipping options up to £200). But the minute the cart weight total EXCEEDS 150kg, then zonetabletwo comes into play, putting the appropriate charge on shipping.
The beauty of this system is that the conditionals govern whether one, or the other, shipping modules are offered at checkout. If the shopper's weight criteria fulfil one shipping module option, the other does not even show up at checkout.
Let me know if you're interested...
SEE IT IN ACTION at https://www.edutrade.co.uk where I have done this to invoke Royal Mail First class postage (up to 2kg) then Parcelforce (over 2kg). Fill a cart with products where the shipping weight is LOWER than 2kg, then click ESTIMATE SHIPPING and then add a few more items to get the weight over 2kg, and then estimate shipping again.
