How do I contact someone with executive resolutions?

To make a long story short, I had to order a new sim card for the device on my account. In the process of ordering it, the representative convinced me to add a digital line in place so I could get the phone up and running in the interim. I was told it would be $15 to get it up and running, so I agreed. Since this account is on auto-payment and my soon to be ex pays the account, I didn't think much more of it after I provided the new sim card to her. Several months later I'm now getting a notice stating that the account is a very large amount past due. After speaking to my ex and looking at the account, I'm now seeing that the virtual line they added is racking up charges in excess of $300 a month. Had I know that this was going to happen, I would have never added this line. I had an unlimited plan on this account. No one in their right mind would add something like this had it been explained properly. I called and spoke to a rep that told me I must pay the fees and that she could only get me a payment plan. I really need to speak with someone at a higher level that can help me with this. This isn't an ethical business practice by any standard and I need some kind of resolution.