Unauthorised credit limit

I’m really not happy with mr Price when you are going to open an account there’s a section whereby as a customer you are if you want an automatic or informed credit increase and I selected informed but, they then increased it from 1750 to 2100 and I called them and asked for a reduction and they promised that they will do it that I wished to informed first so they were sending me text informing me about a credit increase but I ignored them and then they went ahead and increase it. I wish for it to be reduced back to where it was when I opened the account and I don’t wish for any credit increase until I say so.