Harrasment by African Bank

I took out a loan from African Bank a year ago. Repayment went well, but I could not repay the last few months. I tried to make a decent arrangement to repay an amount of R4000 a month starting from 15 November and adding R1000 to the amount every year in April for 3 years to pay back R7000 a month. I can't do anything more if they do not accept the arangement. These people are phoning me every hour while I requested them not to call me before 15h00 as I have a dangerous job that does not put only me in danger but also people around me. Collecting debt I do understand but harrasing people is something totally different. Phone anyone on your contact list every hour, and see how long it will take to irritate them.