Can they change charges after sentencing and while on probation and if so, can charges be changed or dismissed during probation?

I'm depressed and innocent but I have a question about what charges were brought upon me. At presentencing the judge reduced my a&b to simple assault and dismissed one charge. I was sentenced to one year probation. I thought everything stayed the same but I got a notice in the mail of my next probation appointment and on it was listed aggravated assault. On my probation order form, it says assault. I don't know why this is happening to me. No one was ever harmed on the scene. An off duty sheriff was there and made up some lies. I'm a good person and my life just got ruined.