Desperate attempt to get more subscription money from clients.

Was told twice to pay R30 extra monthly on my subscription so that I won't have to pay R600 for their technician call out fee when the electronic devices they installed on my vehicle malfunction and I said no in both occasions. Now all of a sudden my subscription is in arrears that will require them to debit R30 extra on my account for the remainder of the contract. So basically they I will have to pay the R30 they so desperately need whether I like it or not. Their business ethics suck!