Repair of oxygen concentrator

I purchased the oxygen concentrator from limitless health, fully paid prior to deliver, I sent proof of purchase. A few weeks later the machine was giving problems I contacted them and they came to collect it. Once it had been repaired they refused to return the machine as they accused me of not paying for the machine at all. I had to resend proof of purchase , I was then accused of paying into the wrong bank account because they could not pick up any such payment on their records. Only once I had sent them proof of payment into their bank account they were willing to return it and promised to reliever on the same day. They did not follow through with their promise I had to contact them the following day to express the urgency of the situation and only then did they deliver it. Absolutely unacceptable