Do you have their modem installed, or one you own? If it's one you own, call them for a modem self-install kit. There's no charge for it, so you'll then be up to date. If 100 is in your area, it'll then go to that speed.
Yeah, my parents' house is still getting 30Mbps even though their area bumped up to 60Mbps years ago. This is because I had them by their own modem back when Charter used to charge a monthly fee to rent one from them. It definitely paid for itself before Charter removed the rental fee but now it's outdated and holding them back. I've been meaning to go into our local Charter office and get them an up to date modem but until recently they weren't streaming any video or doing anything that needed more than 30Mbps.