So long story, I'm struggling with inconsistent speed almost weekly

So long story, I'm struggling with inconsistent speed almost weekly. I have had numerous cases logged and then I was told to pay a R1000 for an external antenna to help my router to connect to a further antenna. This was now feedback from the engineer. I then asked for Supersonic to please come in site to see if this will resolve the problem before I pay that amount of money for something that won't work. Today 2 weeks later Im just informed that they don't test stuff like that an I just need to buy or not buy the antenna thats that. What if I buy it and it doesn't resolve the problem, do I get a refund. Or are they just not willing to solve problems and sort out their paying clients?