Surely this can't be right?

I'm using Quickbooks Premier 2015, and I tried this afternoon to file my VAT but was unable to do so for the first time ever.

While I realise that Intuit have recently ceased support for this version, the software is the same software, and the online filing doesn't go through Intuit's servers; it simply connects directly with HMRC. Hence the VAT filing  should continue to work regardless of Intuit's lack of product support.

Furthermore, while Intuit's sunset policy pages do indicate that this version won't support the new 'Making Tax digital' protocols from April 2019 onwards, there is no indication that the current filing system should cease to work at any time before then.

Please can somebody explain what's really going on here as a matter of urgency, and advise how this problem can be resolved so that we can continue to file our VAT returns online?