SDT is onto something
if you didn't agree to anything, did not sign a work order...you never authorized anything to be done in the first place if you didn't sign a repair order. Thus, you also did not legally agree to them charging you for the fluid/filter.
BUT--with that said, it'd be a lot easier to just pay it and go on with life, than to get legally involved. The legal system is broken. I am going through it now with a car. I mean, absolutely broken--and you can thank attorneys for it. Car in paint jail, nothing done on it in 9 months (just sitting). I go get it, with the sheriff. I already paid the shop owner 1/2. Took him to small claims, and was granted a judgement for the amount I paid + court costs. 72 days later I haven't seen anything. Called courthouse, said I need to hire an attorney to get the judgment and even then there's no guarantee based on this and that and the other (stupid legal mumbo jumbo). So....what's the purpose of being awarded a judgement in that amount, if they won't award me? Stupid system!! This could (and probably will) get ugly before it's said and done!!