Overcharging on account

I have a fixed line with Neotel and there have been a number of issues with Neotel since I entered into an agreement with them. My most recent one is trying to get them to credit my account for overcharging me for 2 months in a row. I previously have this issue and if the terrible call centre agents would check the history they would see this. I first spoke to Richard who actually , just put the phone down, second time, I spoke to someone, didn't get his name, He told me that it is normally for Neotel to charge, because I could be downloading something and they allow me to breach the 15 gig Threshold to complete my download. I have never heard such balony in my life. I expect someone to contact me and resolve this, because, your service is only getting worse and worse. Next step is to take to social media and open up a can of worms.