If you have a mortgage, then your deeds are with your bank/lender. If, as should be the case, the Deeds are back with your bank then your solicitor will not have these stamp duty details. If your title is unregistered, the details of the stamp duty will be printed on the Deed. If your title is registered, then you will need a copy of the instrument from the Land Registry.
If your last solicitor does not want to deal with you ( and I have some (former) clients that I would never act for ever again after the carry on, the histrionics and the rudeness I encountered although I would ring them to tell them that!), you should talk to an accountant or another solicitor.
mf