Hi Olive
Your question is slightly confusing 'put into the ESA WCA work related activity group'
Legacy CB ESA and New Style ESA provide payment of Class 1 NI Credits, UC provides Class 3 which can only be used for the State Pension.
Yes you need to supply 'fit notes' until your workcoach tells you not to send in any more.
Gary
Nothing on this board constitutes legal advice - always consult a professional about specific problems