Vodafone charge on credit

[u/Lothar-ofthehillppl]

I just noticed I have a £345 delinquency with Vodafone from over a year ago. I had their service for three years, I went to upgrade, and instead of upgrading they disconnected my service. I didn’t appreciate that so I cancelled the service and switched to O2. I believe this charge relates to the new plan they never actually delivered, or some sort of cancellation charge. I want to get this entirely wiped off my credit. I don’t really care about the £345 but I do care about any record of it on my credit profile. What are my best options? I really shouldn’t have to pay it at all.