Yes Sunomo, I am in the same position of having opened an Stocks & Shares ISA with IG in the 2019/20 tax year and then have had the same blocking message when trying to open another with them in this new tax year of 2020/21. Regret that I don`t really understand Charlotte`s kind response - do you? My best quess is that only one such ISA can ever be held with any one provider so am having to start from scratch researching outside of IG for a new account.
Appreciated that you asked this question. Good luck.