Is It Safe To Just Stop HRT Course Suddenly?

I have had the pros tap injection, first the one month one, then the three month one, I was put on a 3 month HRT COURSE HOWEVER I Have today finished my last HRT tablet and I have not had the next injection, I was supposed to get a letter for the date of the next pros tap injection but it hasn't come. Is it ok to just stop everything, the injection and the HRT ? Many thanks for affording me your time.
Regards Jean