The same thing happened to me when had mr for DLA , I never received letter to use for appeal.After phoning finally got letter. Mrs Hurtyback is correct the one month was from the date of letter that DWP finally sent out.
The following user(s) said Thank You: Gordon, Noel
Update is that I've still not received letter regards N MR decision , called again which is 3rd time to be told there is no decision or record of the my request for letter so I can appeal.
Today the lady was very dreary if that's correct but was not helpful so said she will send letter out after she told me nothing on system??
Then had me on hold to come back & say she passed it to a manager??
I have run out of steam/ energy and now understand why people don't fight back!!