You can even use twist-on connectors for the RG-cable.
Cut a short piece of what you dug up, and take it with you, so you can match to the correct connectors.
Buy a small box of RG cable and some connectors. Usually the box that the connectors come in will show how to strip it, leaving the proper amount of insulator, conducter and shield.
Cable companies are notorious at burying to unrealistic depths 1" to 2" is a norm with them. one of their best tricks in a new neighborhood is finding out they are using sod and coming out just before the sod is layed, running their lines on the dirt, with only a layer of sod covering. They will tell you they are making it "easy to fix". Sure, and much more easy to damage it.
TelCo typically buries jointly with power and is usually a min of 24" and in some case 36" (Varies by area, terrain, frost depth). As was mentioned, builders have been known to change grades after-the-fact, which can lead to shallow utilities. I have also seen the opposite, where the phone & power lines ended up 12 feet under when a builder decided to backfill what were going to be walk-out basements due to some building code issue.
As was mentioned, call before you dig. Do this once, they will mark your utilities, then using a copy of your property survey, make yourself a small map to better help avoiding them at a later date.
Finally, force the cable company to come and bury their line properly.