LoisCroft wrote:
Me: I was wondering if it was possible to increase my internet speed.
Him: Yes, you can increase from 4 to 15.
Me: Great. What is the cost of that?
Him: There is no charge.
Me: Wonderful! Go ahead and do it please.
English is not always specific and can be taken literally. Your question asks about "increase". Then, the cost of "that". "That" as well as "increase" can both be referring to either the cost of increased service OR cost of making the change to your service. Obviously, the CS rep took it to mean cost of making the change. And it's further propagated by Go ahead and do "it".
Not saying that anyone is wrong here. However using a pronoun to refer to something in a previous sentence during a two-way conversation is prone to error. Especially when one of the speakers is non-english.