I would be very careful about backing a large anyting into this cable box. Unless and until you can prove it is there illegally you would be well advised to work with the company to get it relocated. If you damage it, you might get a big bill for repairs and your neighbors won't be happy either when they don't have their TV.
I work for a large utility company and it may be entirely possible to relocate this box, but it may not be easy to do and it may be expensive.
Does your survey show an easement along this route? If so, then I suspect that your best option would be to request that it be relocated or buried like the other utilities. Cable TV service pedestals, however, must be easily accessible to provide service to customers and are usually above ground.
If one of my customers wanted a pedestal moved, for their personal convenience, they would be asked to pay for all or a portion of the cost to move the pedestal. Talk to the cable company and see if they will work with you. Ask to speak with the engineer that handles your area. If they "stonewall" you, take it up the line in Customer Relations.
"Never argue with stupid people, they will drag you down to their level and then beat you with experience." - Mark Twain