Cactus 2, you have my sympathy because this is an issue that is not going to disappear anytime soon. There are some coping strategies.
First, the person you were when you were sucked into a scheme is not the person you are now. You are now older and hopefully wiser and can view the position with some detachment. Do so.
Second, chances are that you were sold the scheme by a slick and commission hungry salesman who cared little for you or your circumstances. You are not the first, not the only and will not be the last to be taken in by the unscrupulous and sometimes perhaps borderline illegal tactics.
Third, you were doing what thousands of others did. You did nothing unusual and you are not unique.
Fourth, HMRC has made a complete mess of the enquiry process and has in some instances acted outside the law and outside their remit. As their tactics become more desperate, they are resorting to 20 year retrospection and the like. This is not your doing and unless you join a group, there is little that you can do about this personally.
Last, there is now a deadline - 5th April 2019. By that date almost all the outstanding issues should be clear or at least defined and you will know where you stand and the uncertainty will lessen.
Anxiety is created and feeds upon a fear of the unknown. Read these pages. Speak to professionals (most will give you some free time). Arm yourself with knowledge. If you wish to, join a group. Take positive action and don't be a passive victim which is what HMRC want you to be.