Terrible before and after sales service - and breaks into property to erect wall!

Incomplete quote for installation of precast walling. Was not informed of full details of cost - paid deposit. Missed appointments AND after cancelling with the company, they arrived at my premises without an appointment so told them to leave, *******ly gained access to my property via my neighbour and went ahead and erected the walling. Now insisting on the balance of payment but cannot get any responses from the company to my queries after numerous emails and now THREATENING TO REMOVE WALLING!! No warranty provided, no details of costs as requested.