Just goes to show the power of the ex. Or your handbrake was as poor as most of our ex's. I understand they are prone to the cable stretching.
If your handbrake worked sort of ok before it may be worth just winding the adjuster first to see if this works. The shoes sit in a drum which is additional to the rear disc brake, and so just used for handbrake. To adjust them look on the plate behind the wheel and at the bottom you will see an oval rubber grommet. Take out the grommit and you will see a spur type wheel. Use the end of a flat screw driver to lever the spurs around. This winds the shoe in or out depending on which way you turn it. If you have the wheel off the ground whilst you do this you can tighten until you feel resistance on turning the wheel. Make note on which way you turned the spur as the other side will be the opposite way.
If you don't feel competent to do this it may be worth finding a local friendly mechanic to do this as will only take him/her 10 mins to do.
One thing to remember if you, or a garage are jacking up the car is that the self levelling need to be swithed off using the switch behind the panel in the boot.
Also as this car is new to you it may be worth checking that the jack and the wheel brace is also behind that panel, the 2 rods are behind the rear seats and that the mechanism to lower the spare is not siezed. Also if you have locking nuts check the key is there and in good condition. Best to be prepared if you out in the wilderness.
Personally i carry a breaker bar with the right size socket for the wheel nuts as i've never got on with factory supplied wheel braces.
If you go down the replace the shoes route you may be better offer buying the shoes and the small parts kit yourself then getting a competent brake person to do the job. (£27.95 for shoes and £22.50 for small parts plus some postage @ jeepchryslerparts 020 8200 5500. These are prices on their ebay site but on the phone you could try and hagle by saying you will sing their praises on this forum. Thats what i was gonna do if i needed these parts).
Regards