Cellc unprofessional and unclear terms

I have an issue with how cell C conducts their business, my 24 months contract ends on the 31.03.2021 and I called them on the 15th to notify them of my intention not to renew.according to the consultant I had to call 30 days prior to the end but the contract does not state such and the contract clearly states the last day of the month is end March 2021 really unprofessional I really don't know why they issue contracts if they are not going to honor them.