"In the last month" vs. "last month"
Solution 1:
Today is October 12th.
If you say "I have seen the movie six times in the last month", you have seen it six times since September 12th.
If you say "I have seen that movies six times last month" you saw it six times in September.
Also... you should not mix present perfect with a time phrase. "I have seen that movie six times last month" should be worded "I saw the movie six times last month". This is because present perfect has a connection with the present, but last month is past.