How can I force landlord to lower my rent?

My landlord has been overcharging me for the past five years. When I signed the contract the owner of the place was different and I was in desperate need for a room. The former landlord offered to "rent" the utensils and some furniture to me as well as selling me the bed that was already in the room. After moving in I found out that all the utensils and furniture he was renting and selling to me were actually left by the previous tenant and not his, and that the former tenant was not actually getting any money for the bed that according to the tenant "was being sold to me by the former tenant". After a year or so of living here we got a new landlord and some new roomates. One of the new roomates informed me, a few months after moving in, that his rent was too high and he filed a complaint with the landlord about this through a lawyer and got his rent reduced as well as a return of the difference for the previous six months. I tried to do the same by checking how much my rent should be on the government website that regulates this and it turns out I am paying about 50 euros more than I should, and on top of this there's still 10 euros extra on top of my rent from "renting utensils" that don't belong to the landlord. I sent an email about this to my landlord claiming that my rent should be lowered and asking also to stop renting the utensils and furniture in my room, I said they can take them if they want but I no longer want to pay for them. My landlord never replied and at the moment I was scared to seek legal action about this because I thought the landlord could kick me out. It's been a few years now and the landlord keeps increasing rent over "inflation and service costs" even though I am barely home to consume that much water or electricity (and the wifi is useless). Also, when I moved in me and my roomates (some still remain living here in the same place) were told that rent also covered cleaning services but we haven't had anyone coming to our place to clean up for years now and the walls are getting moldy so we've had to take care of the cleaning of the house also (which is not a problem except for the fact that we're paying for it). I would like to have them reduce my rent and return the difference for the past few months but when I tried to reach out to them about this they never acknowledge it and I don't have a lawyer to back me up on this.