Self-driving Tour of Phuket Attractions

Let's talk about picking up the car first: we arrived at Phuket Airport at 10:30 PM to pick up the car. It took us a long time to find the pickup point. Although my wife and I are not very good at English, we felt confident that we could manage basic communication. However, the Thai front desk clerk's English was very poor, and he seemed quite impatient with us. While we were talking, a Latin American couple came over to ask a question, and suddenly he became all smiles and very attentive—it made me feel sick. Initially, they charged us a 10,000 THB deposit but later informed us it needed to be 20,000 THB, so we had to pay another 10,000 THB without any apology from them. Thinking that the deposit would be refunded anyway and not wanting to keep our elderly family members waiting, we paid the 20,000 THB deposit. After 20 minutes of hassle, we were finally able to go to the smoking area and get the car. Now about returning the car: Our flight was at 8:55 AM, and we had arranged to return the car at 6:30 AM. Upon arrival at the airport, staff came to check the car. My husband and I split up; I went to the counter with the deposit slip. Here's the funny part: all the rental company counters had people except ours. I called the two phone numbers from our reservation, but both were disconnected. The number on the counter sign was the same and also disconnected!!! I had no choice but to ask the lady at a neighboring rental company to help contact their staff, who told us to wait. Thirty minutes later, no one came. I asked the lady again to call, and they said someone was coming. Another half hour passed, still no one. We had been waiting for an hour with our six family members. The guy who inspected the car came over, but his English was poor and he didn't speak Chinese. He probably sent a WeChat voice message to the counter staff, and then handed me the phone. I explained that I just needed a stamp or some proof that the car was returned in good condition so that they wouldn't deduct from the deposit later. The person on the other end kept repeating that the deposit would be refunded to my bank account in about two weeks. Frustrated, I raised my voice and reiterated my request, and the caller simply hung up. What kind of service is this?? What attitude?? I then told the inspector that we had been waiting for an hour and were very upset. He called the Chinese-speaking customer service, who informed me that there were no further procedures and no proof would be given—we just had to wait for the refund. Fine, since the higher-ups said so, we left. However, when we entered the departure hall, miraculously, the counter from where we picked up the car was staffed. My husband went over with the slip, and the clerk finally stamped it, confirming that the car was returned in good condition, and the deposit would be refunded. So, my question to the Chinese customer service is: if there's no further procedure, what was that stamp we got at the departure counter all about?