courier guys issues paying extra

I am not sure what has happened to this company but its truly getting bad, This is not the first time I use them often now iam getting charged extra all the time and delaying my packages and no body at the call Centre can help. This seems to be a new thing that the machine calculates the package sizes and it cost more than double than what was quoted, seems like they trying to make more money when the package is in there possession which makes them strong arm you. This will be the last time I use them as I do not see that huge difference in the package and then huge difference in price.