As regards the current sale complain in writing if you have not already done so.
Write a letter to the senior partner (or complaints partner who should be named on the first letter you got setting out costs etc...) setting out your grievances and stressing the urgency and what you've heard about the buyer being advised to pull out. Try to back things up with examples.
Try and include the relevant details in your heading ie your name, address of the property, their reference if you have it and the nameof the person dealing with your matter on a day to day basis. It is better typed than handwritten.
Try setting out your issues point by point and ask them for a written reply responding to each point in writing within 7 days due to the urgency of the transaction.
Give your contact details in case they want to discuss the same or to speak to you in person but explain if you are not contactable in office hours as for example you are at work.
State that if you do not hear from them within the 7 days you will copy your letter to the Customer Complaints service at the Law Society.
You can find their details here...
http://www.lawsociety.org.uk/choosingandusing/ redressscheme.law.
You could also stress that you had used the firm previously and been very pleased and that it is a shame that it has come to this etc...
Make sure you keep a copy of everything.
If the sale falls through I'd consider instructing new solicitors for the new sale, explain the situation to them.
They may take it on and agree with your current sols to discharge their fees on the sale (subj to negotiation as to the fees to be charged if there are any grounds for complaint).
All docs can be sent over quickly and easily and if the current buyers