From what you say, I suspect you are a victim of wheel clampers targeting sites, with the land owner receiving a percentage of the fee. The motoring press has reported on this over recent months.
To maximise their return, the clampers park other cars on the land � in an attempt to give the impression nothing untoward will happen if you park there. If this was their mode of operation, you should have noted that yours was the only clamped/towed car on the lot.
What suggests to me that you are a victim of such a �scam�, is the speed with which the tow truck arrived, it costs money to run one of these (plus the staff costs). Once you parked and left your car, a spotter would have called for the clamper/tow truck and �330 was �earned� for 15 minutes work.
If so, needless to say that there is no chance of you getting any refund.