Debit order from R199 to R799 without consent or notification

I have been a member at Planet fitness Hennops park for just under a year. August and September they debited my account for R799 in stead of the normal R199 that i have signed up for.

I went in to see if someone could help me with this issue, one of the staff they checked the system and said my rates was increased because I didn't go 12 times a month. (This was NEVER discussed or mentioned to me when I signed up)

I have trained 5 times a week until our daughter was born, she was born pre maturity and we have had lots of health complications

I reversed the two debit orders of R799

Now i recieve a threatening sms sayning that they will take legal action against me??? Not even the decency to call me?

If this is not resolved asap i will cancel my contract and join Virgin Active as they are much closer to my home