Hello,
Yes, they are releasing new songs in addition to songs released from their album M.A.D.E. As for your question, '에라, 모르겠다' is actually a bit difficult to explain--it means something along the lines of 'Oh well, I don't care/I give up (Literally it means 'Oh well/all right, I don't know')', and is usually used to express resignation when someone is giving up on something after giving it some effort.
Hope this was of help. Please let us know if you have any other inquiries.
Best,
Lyn
Team KoreanClass101.com