I'm not sure if you really meant this as a reply/rebuttal to the grandparent, but contesting a charge with your credit card company rarely ever results in "nastiness in court". In fact, that's pretty much the one virtue of credit cards over other forms of payment - it's easy for you to contest things and then your credit card company will usually just take care of it for you.

The could also find a fax machine or a telegraph. It's not the user's job to jump through hoops -- stopping the service shouldn't be harder than starting it.

I recommend this method. Give them a chance to do the right thing and let us hear about it after.