Submitting a VAT return to HMRC is your responsibility or the responsibility of your tax agent/accountant.
Fly Software are not responsible if you forgot to submit a VAT return, if you submitted incorrect figures, or you ignored notifications presented by Easy MTD or Easy MTD VAT during the submission process. With regard to the latter, if an error had occurred during the submission process (e.g. the HMRC system failed or your Internet connection stopped working), you would have been clearly notified by Easy MTD or Easy MTD VAT and provided with an opportunity to try the submission process again. Furthermore, the associated open obligation would remain in the Easy MTD or Easy MTD VAT interface, and a fulfilled obligation would not have appeared - both of which are a clear indication that HMRC did not receive a VAT return.
The associated open obligation should still be visible in Easy MTD or Easy MTD VAT so please work your way through the submission process at your convenience.