This will take a few times but... That is when you interact with them, maliciously. Basically cost them time and money. Have them on there for an hour or more. Set phone down come back every 2-3 mins and make sure they are still there. Make sure you have them repeat everything, your connection is not so good. Drag it for at least 20-60 mins. Then at the last second back out on the sale and mention you wanted on their do not call list at the end. As well as a copy of their DNC policy priority mailed. "you know what I am going to ask you put me on your do not call list and I want a copy of your do not call policy just like the last 3 times".

You break that support persons numbers and they may add you. At worst they will call again and you cost them more money.