Disposal of garden refuse dispute

Hi 

I recently paid for my garden to be partially landscaped and part of this included having rubbish taken away from my property and disposed of by the gardeners who were employed and have been paid. 

Unfortunately they have abandoned the trailer with garden waste and waste of their materials on the next cul de sac near to my house, which is a leasehold street. Having tried to get them to remove it they have blocked my number, and coincidentally the owners of the leashold knocked on my door making enquiries as to the owners before I notified the council. I offered all information I had on the owner of the trailer but have since received threatening emails from the leasehold owner's solicitor who are advocating that the contents of the trailer still belong to me and that they will contact the police, dispose of the contents on my property when removing the trailer and make me responsible for any costs incurred. 

My response was that as I paid them a sum of money for this to be remove and that rherefore the contents of the trailer left my property it is the responsibility of the gardeners to dispose of the rubbish or incur and criminal/monetary charges. Can anyone advise of my rights in this situation?