Overcharge by service provider but they give me dispute forms

Bad service with fnb I went to branch for help service provider overcharge me suppose to pay R18 they deducted R1800 when I went to fnb to assist me they tell me to fill the forms for debit dispute while was not requsting dispute. My panic is that forms won't help me I won't get help iven 2022 I feel that forms phone them everyday no help till today that account is over negative balance due to poor service for fnb. Instead of assisting they will say they will investigate forever