Being charged double for postage

Hi Guru's/Zenners,
I have my shipping setup using the zone rates and by weight.

When I attempt to purchase an item on my website and go to the cart, I can see that the correct weight is being calculated but I am being charged double for shipping. Then if I choose to buy 2 of the same item it adds the 2 weights together fine, but am being charged shipping like I have asked it to charge per item and also twice.

e.g.
T-shirt 100g
I buy one and am being charged 4.40.
I choose to buy 2 and am being charged 8.80

For shipping to Ireland by rates are:
100:2.20,250:2.70,500:3.85

I have figured that when I set the weight of the t-shirt to 50g the shipping is correct, but when it its set to 51g it goes up to the next shipping level, so somewhere the weight is being doubled and thinks that it is 102g.

I have since setup the website to use 2 different types of shipping methods, DHL and standard post. By using the Zone Rates Clone mod and the same thing is happening with that.

I don't have any tare charges setup.

My website it: https://www.traditionalcraft.com
Version 1.38a

Please save me!!
Thanks
Al