TOM100
I am also going with TUI to Greece but not until 23rd June 2020 - have not heard anything from them yet and not been cancelled.
I assume your travel was for 1st may 2020 and your refund voucher etc is for a new booking which has to be for travel before 28th May 2020. How can they expect that to be OK we will probably still be in lockdown by then. Or do they know something we don't
Have they offered you any other form of refund ?