Harrassed and ************ to employees negligence

Today I was harassed, humiliated, and intimidated at Ruimsig Post Office by an employee and a manager there(they had no name tags). On my arrival I was going to renew 2 vehicle discs and I asked the lady at the till how much the first disc is going to cost and she told me, immediately asked about the cost of the second one, she was holding a white paper when revealed the first disc cost, turned to her computer to check on the second one. While busy I was asked if I am going to be paying with a card(my understanding is are you using a card/cash like everywhere you get that question ),I said card. Then she turned to her computer again. Then told me about the second disc cost, I then told her that is going to be too much for me wasn't expecting that much, told her I need to make a call and see if I can be able to get more money to pay for the 2 discs. While on the phone without my knowledge and consent of payment she printed out one disc. As soon as I hanger up, I told her I will rather come back later/the following day. To my surprise, the disc was printed and she told me I must pay because she already printed it. At first, I didn't even understand what she meant as I remember the white paper which would not make sense why I would have to pay for a printout on how much I must pay. Then she just told me I should pay, I was puzzled, and when the manager approached hearing that I say I can't pay as I don't have that money and to me, it felt like force. The manager only asked the lady what was the matter. The lady said to her ‘ I already printed’ now pulling the disk from the printer, which now showed me she has made a mistake. The manager looked at me and told me I must pay, I tried to tell her my side but fell on deaf ears as it was now a matter of me being forced to pay through how I was being shouted at and intimidated by the Manager. I even asked what can be done, all was there was force that I must pay for the employee's negligence. I was embarrassed and was asked what do I want there filling forms if I can't pay/afford it. I was so irritated and wanted to walk away. Then I was told she will keep my ID BOOK and put an S mark on my vehicle, if I wanted my ID back I must make sure I involve the police. I left the premises to calm myself down as I was so harassed and humiliated. Came back with my phone to take a video as I realize now I wasn't going to ever be treated fairly. Asked for my ID back as it was now kept against my will and my side wasn't important but for me to rectify their negligence. Security was even called on me, the manager approached me physically because she felt I didn't deserve to have my proof that my side wasn't being heard and force was being used. I asked her to check their camera that there is nowhere I told the lady to print anything, and she dismissed my point but kept on making threats to open a case which makes no sense to me as negligence is in their site.