https://www.whatdotheyknow.com/request/ ... ing-810880
I guess the above link would help unless UKVI changed it's policy which I'm not aware of. May be seniors or moderators would know better but again moderators might only reply to you just to bully you rather than any practical help. Your circumstances and the very idea that you came to this forum to seek help wasn't about the merit of your application but if I'm not wrong then it was to find out why it was REJECTED as INVALID saying you didn't enrol your bio-metric information within the stipulated timeline. If that's the case then the above link might help unless as I said already if the UKVI didn't change the policy.
I personally think they're wrong in rejecting your application without giving you the opportunity second time but please seek professional help to be absolutely sure about it before you take any actions regarding that.
If you find out that the UKVI officials made a mistake by not following their own policy then the next thing would be to write a PAP (as previously suggested) to basically threatening them with legal action mentioning how stupid this mistake that they made by not giving you a second bio-metric enrolment letter and also telling them that a judge would just throw the UKVI's arguments if they have any & also to support that you have the sick not as an added bonus (Regardless of the sick note, they had to send you another letter if the first wasn't enrolled).
Now the most important part would be to make a SET (LR) application within 10/12 days after receiving your Rejected application even though you've not completed the required time (even with minus 28 days) but I guess by the time you would enrol your biometric you would have completed your 10 year even may be the full 10 years and so when the caseworker actually taking a decision on your set (LR) application, they would find it really difficult to refuse it as you would have completed your 10 years at the time of taking the decision.
In the meantime, if the GLD (Govt. Legal Department) replies to you with some senses as these are lawyer within GLD & not just some A level graduate Caseworker that they accept of their mistakes & would give you an opportunity to enrol your bio-metric again if you so wish then you should reply to them saying that you've already made another application for SET(LR) which they should now grant instead as you would have certainly completed your 10 years (minus 28 days) by the now if the UKVI didn't make the stupid mistake and finger cross that should be the end of the matter & they grant your ILR.
If you only challenge the FLR HRO rejection by the way of writing a PAP to them and not making any SET (LR) application then you'll put yourself in danger of not be able to complete the 10 years at all ever as you would loose the 14 days grace period that could be used for only one OUT OF TIME application and considered as if it was made in time.
Your only hope would remain winning the argument of the FLR HRO application rejection but God Forbid if that goes wrong for whatever reason then you wouldn't be able to complete 10 years either.
Now, trouble with the above scenarios to follow that you would have to prepare yourself for a lot of money (Deliberate policy created by the Hostile Environment) which isn't easy at all as we all been there. you would get your FLR HRO money back as it wasn't refused but rejected rather and also get the Premium services money back as you wouldn't attend (minus some administration fees) but these refunds could times and you would have to make a new SET (LR) postal application almost immediately which would again cost you money. I'm really sorry that the Hostile Policy put you in this situation but the above mentioned scenarios are the best way forward in my opinion ( I may well be wrong & I do apologise in advance for any more trouble I might cause)...