How long to update experian credit file?

Hello, does anybody have any idea when experian update their files? The only negative on my file is that I am not on the electoral register, so in late March I filled in the form and registered, this was followed by a letter confirming that they would enter me on the register and 2 weeks ago I received my voting card. Confident I was now on the register I checked my credit file with Experian and lo a behold it still shows that I'm not on the register!!
My question is does anyone have any idea if it is normal to wait 2 months for file to be updated?
Has anyone else experienced this?.

Thanks in advance for your time in answering this.