Conveyancer/mortgage advice

just looking for advice with a house I’m close to completion on as a FTB. Got my offer accepted 8th August on the house and they’re classing it as an ex new build. My solicitor has had back and forth with the sellers solicitors apparently over queries since I appointed them, up until they submitted everything to the lender (nationwide) 23rd December. they said they don’t submit all documents to them until they have everything, which I can understand, but we’re now going into Feb and the go head from Nationwide is what’s stopping us getting to completion! All of Jan up until now my solicitor has been back and forth with them over questions from what my solicitor has submitted. I believe my solicitor has been giving them half the story, they ask for things and she doesn’t explain it fully so this adds delays as nationwide come back asking the same thing again but in a different way. But my solicitor is also speaking to someone from Nationwide who’s been passing her emails onto this property policy team and we have to wait for their reply each time which adds to the delays also. I was expecting today to get a response that we’ve got the go ahead but they’ve come back asking more questions. It was about the planning conditions not being discharged but it’s due to the site still being built on so my solicitor suggested indemnity insurance, yet they’re now coming back (nationwide) asking about the pre-occupancy conditions. Why couldn’t they have put this in their email 2 weeks ago! The sellers are pushing estate agents for updates and wanting to get nationwides go ahead by Friday or they’re assessing what to do and potentially pulling out. My mortgage offer ends next Saturday, not sure when the sellers does and everyone’s aware of this but there’s no urgency. This property policy team are unreachable and they can’t escalate responses. I’ve emailed my solicitor back today saying can she phone them not email at 4:30pm and speak to someone directly as now they need to get information from the developer! I’ve said too that thatll be another day and when we go back to nationwide with this info and they come back we’ll have lost another week and then what happens when they come back with more questions?! I’m at my wit’s end with it all and just don’t know what to do. Has anyone had any similar experience with this nationwide property policy team and why they’re asking all this at such a late stage?