Generator issues not a happy Customer at all

I bought a Ryobi R2700 generator on 25/1/2023. It was a demo models as they did not have any stock in store, this generator was on special for R5500.00 at the time. they did put in my petrol and the required oil. they started it for me, work ok according to me, got home, my husband said the generator is not running smooth, the voltage is jumping the whole time, I did at the time only connected by desktop PC to it, so it was suppose to run smooth as it was not overloaded. my husband took the generator back on 23/2/2023 and complain that the generator is not working properly. Builders Express send it to someone to look at it, I assume it was Ryobi, it came back the next day, it still sounded not perfect but they said there was too much oil in which they drained, as I mentioned they did put in the oil, not us as the customer. we are still not happy with the generator as you have to pull the chock open in full, the voltage is still jumping and we took the generator back again today, we rather insist on having a new generator from the box than this demo model which is not doing the job for me. Ryobi did confirm they will test it again, but they do not exchange for a new one, they will have to give me the credit I paid for it, if it is faulty thou, but if they believe the this is 100%, I am stuck with this generator making a huge noise, using so much petrol and how long is is going to last,

I am so unhappy with the service I am getting, Charles, the store Manager is understanding, but I do not know how far he will stand by us as the customer to accommodate us with this dilemma.

I bought a 650w Fragram 15 years ago, still running like when I bought it, I just wanted bigger to accommodate my fridge during load shedding.