How can I get PlusNet to take more money from me?

[#1]

I am posting this here in a vain attempt to get this fixed.  I pay for my broadband and an extra £1 for my domain.  All has been fine up to VAT change.  When VAT went down to 15% all was OK, but since it returned to 17.5% I have only be charged for my broadband and not the extra for my domain. 
Latest joke in this long running saga is PlusNet have just issued me a £1 credit note!!!
History is -
12 February ticket 32013309
6 March ticket 32372295
7 April ticket 32854195
Is there any hope that someone within PlusNet can actually sort this out for me?  I think I have been told 5 times it has been fixed.

[#2]

Hi there,
I've raised a problem internally, passed feedback back for the agents who have dealt with this so far and have updated your ticket.
Sorry for the issues so far.

[#3]

I think I have now been told 5 or 6 times this has been fixed.
I have just received my June invoice - still wrong, it is £16.49.
To date nine different people have looked into this matter for me.  Please would someone else now look at it?

[#4]

Hi there,
The problem I raised hasn't yet been fixed (it's currently in testing), as soon as that's sorted I'll let you know.

[#5]

Would have been a nice touch to let the OP know in advance that it hadn't been fixed yet without them having to wash PN's dirty linen in public yet again

[#6]

There's a ticket on the account which has updates on it.
I was just advising here for completeness.