Repair visit $100 charge.

I moved from one location to another and found that my internet kept dropping off and coming back on at least once every hour or two. I called customer service and was told they would send out a tech but that I would be charged if they found that the issue was with my equipment or installation. I was rest assured by the agent that I wouldn't be charged otherwise. Tech came to the new residence and said the quality of the signal coming into the residence was poor and that he had to boost it by adding a device to the end of the cable. He said he also replaced the cable that came with my modem. Now, why he replaced the cable beats me since this modem was pretty new. He also assured me there were no issues on my end, but with the signal coming in, he said he had created a ticket so that the outside box would be looked at. Alas, I find a $100 charge on my bill. This seems pretty crooked to me. I have never had an issue with Cox until now.