Poor Service

I joined One plan Insurance 3 months ago, I was offered a premium for myself and my 2 kids, which I was happy to pay - I received really good service during the application process- fast forward 2 months down the line- I go onto the live chat, a service offered by one plan(which seemed easy, quick and efficient) I enquired about removing my son from my plan, as he was going to be covered on his dad's medical insurance. While chatting with a consultant, I am offered the new premium amount, we confirm this amount, both via the chat and email confirmation. fast forward to the date of debit order, an amount greater than the aforementioned premium is deducted, I call one plan to query- I am told I was given the incorrect amount, not only via the one plan chat- but also via email. All this after the deduction, after insisting, i was offered a chat with the manager Steve, I was hopeful as Steve assured me a speedy investigation and an even speedier response - another month has passed - still no feedback from One Plan.