Removing Domain Hosting

[#1]

For the last couple of years I have had my domain registered elsewhere and Plusnet setup for hosting only.
However I recently decided to setup hosting with where I have my domain registered. I have removed the forwarders to Plusnet, but for some reason I'm still getting emails twice (I'm assuming one from Plusnet and one from my provider) . When I log into Plusnet I can see that they still have it down has hosting my domain.
How do I remove the hosting from Plusnet as I cant transfer it out as they never had the registration in the first place?
Also if I remove the MX record (mx.last.plus.net.) from the DNS will that stop any email being relayed by plusnet?

[#2]

What Nameservers are you using? It does not matter you see PN hosting your domain if the nameservers are pointing somewhere else.

[#3]

The Name Servers on the Host point to the following
ns1.livedns.co.uk
ns2.livedns.co.uk

The mx record points to mailserver.tomcat31.co.uk (priority 10)
On plusnet I only have an mx record of mx.last.plus.net. (priority 40)
I think it maybe the two mx records that are causing the duplicate emails I'm getting. If I go to remove the MX record I get the following message
"Are you sure you want to delete this DNS record?
This is your last MX record. If you remove this record you might not be able to receive email on this domain until another MX record is added!"
I want to be sure that this will resolve the issue before I remove it.
Regards

[#4]

No it will not resolve the issue.
You need to check your MX records for your domain by using http://www.mxtoolbox.com/ this will return the nameservers it used and all the MX records in use. It's more than likely that you still have a mail forwarding active at your hosting provider.

[#5]

The records only show those of my hosting provider (see attached) and there no forwarders set up
I'm pretty sure that the duplicate emails are coming from Plusnet but I would just feel it would be easier if I could remove any trace of emails to my domain from Plusnet so if it continues then I can take up the issue with my hosting provider.

[#6]

You need to look at the email headers to see where they are coming from.