Hi zeeteecee, my first thought is maybe someone else wants the field and is making life uncomfortable in the hope the present occupier will move on.
Piles of soil are usually put across gateways to prevent gypsies/travellers moving onto the land. It won't have travelled that far - anyone round there got a tipping trailer, or an owner of a tractor with a clearly 'turned' bit of land?
Regarding CCTV, I'm all for it. Lot's of other benefits for anyone with livestock too as it connects to the Internet so you can take a look at things no matter where you are in the world - even better, you can do it via your mobile phone.
If they can't afford the CCTV right now at least put a CCTV sign up. Needless to say screw it on firmly!
Really hope things sort themselves ok for them.
Best wishes.