Are you speaking to customers on the phone or other colleagues? I was in an engineering company so I would call the same guys over and over again. That definitely played a part in it. It probably took around 6 months. See if your struggling with certain words and phrases. Write all the words down on paper and when it comes to saying it, read it off the page instead of out your head. That helps me sometimes. Stuttering is a real awkward thing because people have tips and tricks that work for them but not for others lol. Try writing it down if you’ve not before. And stick at the job because at some stage, it will hopefully click for you!