In that case either you try to enter on your own and see what happens or you try a safe entry service. I don't see what other options you have other than applying for a proper visa
If you've been denied entry then who knows how long you might need to wait. A ling time if you haven't gone back to your home country. You could try contacting one of the safe entry providers and see if they can get you in, but if they can it will cost
You can apply using one of the soft power options and provide your pension details to show your ability to support yourself while undertaking the activity
It's all a question of timing. You can file a 90 day report up to 14 days in advance and if you do that your next report is due 90 days from your last report. So you could do the 2nd one online
There are far too many reasons to try and cover. The reason I asked is that if it was cancelled it is most likely an issue with your biodata, it could also be the reason for being rejected but usually they cancel in this scenario