HELP ! Please !! Vendor disappear at the exchange date !!! what to do?

Hello Everyone, need your advise! Thanks a lot in advance!

Last Friday:  Real estate agent advised me vendor had accepted my offer.

This Monday: Contract faxed to my solicitor .

This Tuesday: Contract amended on some minor clauses.Both partied agreed, And We signed the contract, fax to vendor solicitor, Vendor signed the contract too, and faxed to my solicitor. And both solicitors had agreed to exchange contract on Wednesday.

From Wednesday till now, Vendor’s and solicitor is out of touch and not returning our calls.

I want to know:

Can I sign on the contract where the vendor had signed and fax to them and enforce the sale?

I had purchased before, what I did before was me and the vendor both signed contract and fax through to each other's solicitor, then the cooling off period starts as long as both party signed on the same contract. . .. in this case, I already have the signed contract from vendor, can I just signed it anyways and fax through and make the sale go through?  I used a different lawyer this time, she said we both signed respectively, then exchange the next day. Which we think it’s fine. But didn’t expect this happening.

What is my options now? My 10% deposit was paid to my solicitor, but not to the vendor as yet.

Waiting for your advise…