New solution following KillaQueens515 PC method as of 2019
KillaQueens515 gave a good method however since about a year or two ago your premium cannot follow to previous months. But I have found a workaround to help speed this grind up.
1.) Make sure you are premium. It is 1.99 membership that blocks ads and give extra coins.
2.) Change date to any prior month.
3.) Open Daily Challenges under your non premium month you chose (ex. Im doing June 2019). DO NOT START ANY GAME YET OR BACK OUT TO MAIN MENU!
4.) Switch the date back to the current date and voila!!!!!!! You have premium for the previous months. Downside is that every game(day) you finish, it takes you back to the current month dates but you just use this method every time as long as you are a premium member.
ALSO from what I heard if achievement don't unlock, just get a medal in current time to sync up with servers.