I bought my bike end of October 2019, the service I had was good. From December I was out of the country for 6 months due to work and then covid lockdowns, and my bike hadn't been used. When i came back and started riding again the chain occasionally slipped so I took it in for a service. The guy said to me the chain was stretched and my cassette was worn.. how??? Its hardly been used. I asked him to check the settings and he said he did. So I should buy a new chain at won85,000 and if it doesnt get better then order a new cassette which would take 1 month. At won208.000 He replaced the chain, from then everything was worse, I couldn't ride using the lowest gears. I had to cycle 40km home. I found a bike shop near where i lived as I wanted a 2nd opinion, he tried my bike, said he knows the problem, adjusted some screws and it works perfectly.