Buildersmate: Advice welcomed please!! (or anyone else for that matter! THANKS)

[Nosha123]

We are building a new build with basement. We are using a basement tanking company and so far they have tanked the external areas and just need to do the internal floor area. They have only been paid for the work done so far.
NHBC state that we must obtain an insurance backed warranty for the waterproofing - which the company do provide at a cost of about £450
We decided to use a waterproof concrete base slab as opposed to standard concrete (despiite their protesations it was not necessary) as we wanted to be absolutely sure there would be no leaks or problems later down the line. The internal tanking has not yet been done (and to be honest I would ask if its even needed as the external tanking and caltite base have made the basement completely waterproof).
My problem is - I emailed the company in July and again in August asking when the next stage needs to be done and what payments would be required - and had no response. I then telephone them yesterday and it immediately went to ansaphone (which it has NEVER done before, their office was always manned). I check on Companies House and they are still in business but next 'Returns' are 7 weeks overdue.
What do you suggest I should do?
They may still return my call and just be genuinely busy - but I thought it odd that apparently they never got my July email despite receiving previous emails.
Am worried - not for waterproofing purposes as I think we are pretty covered - but for insurance backed purposes for NHBC and re-sell...
ANy advice welcome
Thanks

[The Builder]

so ....... you have to pay for their warranty as well as the NHBC................. NHBC seem to want it all ............. anyway, do what Zac suggests. Maybe give them 14 days to be sure. It always used to be known as "The Fourteen Day Letter".
Whoever finishes the job might not be willing to warrant work begun by someone else. If so, one way would be to live in it and enjoy it........... then when you come to sell, employ a surveyor to inspect it and OK it officially. That should be good enough for a buyer's mortgage company.

[Nosha123]

thanks chaps!!!