Bad bikes

I am very very frustrated with Game stores. I purchased a bike black Friday last year for a Christmas gift. Once opened after Christmas we found that there were so many faults such as brake not working, handle bar drops even thought it's tightened, wheels were buckled to name a few. When I returned it I was told it's over the 7 day obf period which I understood also over the 1 month period for some guarantee and the bike needed to be booked in an repaired. This happened on on the 7th of January 2022. Being aware of their 21 working day policy I calculated which the latest day would be of the return of the fixed bike. On the 24th of February I returned to the store after getting no feedback and was told they will check if it's in the store already but I wanted a new one as per their policy. An exchange was done and I received a new bike but that bike also had a problem so I took that back as well. This time around I received a voucher as it would take long for the credit to reflect back on my account. I went to the store on the 2nd of March and spoke to the department manager about the bikes having so many problems and he gave me an option of choosing a other bike which was not the same barcode as I was told to take previously and I was happy that it's another bike and hopefully it would be a good one. After all the struggling to assemble and sort out the brakes just to find out that both wheels has punctures in and my son did not ride the bike once as the brakes was not set yet. What am I to do now? I had a problem previously as well with a bike I purchased there and then just returned it but my son wants a bike. Why are the bikes so bad at this store, is it due to mass production???