Vendors delaying exchange: should I ask EA what's going on?

AFII

I'm worried about a vendor delaying at the point of exchange...

On viewing the house the vendor said they were moving for work - they had to move, and they had a relocation schedule & would be out of the house whether or not it sold. Their stuff was in boxes so I believed them!

I made an offer on a house which was accepted & negotiated slightly lower offer after survey, which was accepted (thanks to reading threads here!)

I signed all the relevant paperwork & instructed my solicitor to exchange last week, at which point I was told the vendor had offered two completion dates. I said either would be acceptable, and I'd prefer the first.

It took ages to contact the vendor - so long that the first completion date deadline came & went, and now apparently they are 'trying to change their mortgage' and don't want to exchange yet because they're not sure how long it will take!

Obviously I am worried this is the beginning of a huge delay, or that they might pull out entirely. I've already booked movers because they'd suggested dates which I accepted!

I've every reason to believe my solicitors are working hard on this, but they aren't getting answers for me. It's extremely frustrating; I want to know exactly what's happening, and whether this is a delay of a few days, or weeks....or months!

I'm half inclined to ring the Estate Agent and see if they've any insight (I've found the vendors on facebook but assume it would be weird stalker-like behaviour to send them a message directly!)

any ideas? Having to relay messages through solicitors seems to take ages, and turn into a game of chinese whispers...