If it's something unimportant, I just don't communicate with them. If they are not willing to sell me something I want, then I buy it from elsewhere.
If it's something important, like me already being a customer and bank losing my money, and there is no communication channel I can use, then I only communicate with them through authorities. If I had more money at my disposal, lawyers can make it work quicker.
Besides, having the communication channel usually isn't enough. Chances are high you are facing a biological chatbot; an actual human person who has no training and no authority to do anything, and who has been programmed into detecting single words like 1980's chatbot software, and then reply something not related to the matter at all.
I have had two serious complaints during the last maybe 5 years, one with a phone company who accidentally closed my phone service completely because of their broken process, and bank who "accidentally" left my old card active when they "upgraded" it into a new card. In both cases, communication was exactly like 80's chatbot, and only after very thorough explanation of which exact authorities and media houses are to be contacted, at which exact dates, only then something started to happen. You need to go far enough to trigger their process of involving their lawyers, and give enough time (2 weeks in latter case) to do that.
I try to avoid using "services" as much as I can, knowing how to do everything myself. It provides a very stress-free life. The idea that paid services make life easier was maybe working in 1960's when this culture started. Nowadays most of it is just incompetence, understaffing, and cost gone through all roofs, and the downhill has accelerated during the last decade.