I have tried the new bionic and to be honest had no end of problems like getting new units getting my old stats back and getting the software to recognise my password.

Your classic stats are accessable on the seti classic site. And if the merge of the both database was successfull, you see it on the "your account" site.
On the account site are only the classic stats from march 15th in the moment.

I have been a member for a lot of years now and the old software was great, non intrusive and easy to run. Why the change? The old saying is so correct especially in this case (if it's not broke don’t fix it!!)

Because the old one had made lot of problems and was not enought flexible. For example cheating, sendig out the WUs up to twelve times - boinc sends out a WU 4 times, they had also a lot of problems on the backend.
with boinc you can now join a lot of differnet projects with one scheduler (=boinc).

I have seen many people on here who are complaining to about bionic many members have had to stop participating at all in seti this seems so unfair.

Please read this post from Matt Lebowski from the seti@home team. It describes the situation of seti@home, berkley and the need for a new software in detail :
http://setiathome.berkeley.edu/forum_thread.php?id=24612#209002

Why don’t you guys at Berkley listen and bring back the old software or you will loose yet another participant and many more I assume.

Never, because classic is outdated and over.
The science parts on the seti app are the same like on classic. But soon will a new seti app with 11 times higher senstiy and a lot of more science computing released.