Sabre didn't mean you hadn't thanked ppl for their time, he's not that kind of person: he was, rather, expressing concern that he felt you were not following the advice.
In that respect let me add if I may a word. You don't have time to be "on the brink" of registering with noddle. Nor is it to be approached like a walk on a tightrope over a river. I urge you to do it today.
And pls don't imagine I know nothing about your illness. In fact I do, but it's irrelevant here. All I need mention is that it's important to act whilst you're in charge.
Preferably to contact the advocacy service too. With most, you'd not be given an immediate appointment as there would be a waiting list, so the sooner you act, the better. And yes, you could show them this thread. Far more use than trying to explain from scratch. Besides, they may not be all that au fait as we are with debt matters, especially the Arrow beast.
No you can't write a letter asking them please will you let me off paying. But if they cannot produce a compliant, executed CCA, there are simple mechanisms to enable you to defend in a way to prevent court action from proceeding. And if you've reached the statute bar, they can do nothing.
Do not worry about losing your pension. That is not going to happen.
Yes, Arrow will have outsourced [their horrid word not mine] to a couple of their concubines but eventually they pass to a solicitor to take action. And believe me, some of those solicitors are nasty. However, we know how to take the venom out of their bite. But we do need your cooperation. Taking 2 to tango, and all that.
Good luck
Oleg