How did you tell your solicitor and make it clear it was provisional?
When did contracts exchange or did your solicitor exchange and complete simultaneously?
How did documents get signed, contract, mortgage deed (if financed that way), transfer etc... and when did they ask for completion monies etc...ie by letter or appointment.
Did they ever give you any indication as to when completion was scheduled (in their opinion) ie in letters, face to face or in documents.
Usually what would happen is that the date is agreed via the parties, often through correspondence between their conveyancers and once contracts are exchanged the date is legally binding unless an agreement can be reached between the parties to waive it.
Any work should be done on your instructions and authority. It's difficult to advise not knowing the whole situation and seeing correspondence and documentation. I'd suggest, if you've already spoken to your solicitor, that you speak to the Law Society Complaints Service and get their advice.
http://www.lawsociety.org.uk/choosingandusing/ redressscheme.law