Hi @Shane
Welcome to the customers help customers Community of Vodafone.
Before I start, I'm not employed by Vodafone but I'm happy to help. In addition, I want to let you know that this is a private community and not a business community. So for business questions and complaints you really have to go to the business department that can be reached via this page.
It is of course annoying what happens to you and find it very strange that a previous owner would have done this because a mobile number may not be active for a long time before it is released again. There is quite a long time in between, so it is strange that you already have these costs on your account. You have stated these costs from the beginning and this from the beginning? Have they already let you take a look at www.payinfo.nl and cancel any subscriptions there? You can read about what you can do about unwanted SMS services here on the Rijksoverheid website. There are some useful tips to follow.
It remains difficult and annoying when this happens to you. Vodafone only applies the costs they receive from SMS code 5030 and they cannot do much about that themselves. But again, I don't work at Vodafone and for the business side you really have to go to the business customer service. Good luck and I hope you manage to stop these annoying text messages.
** translation done in google translate from NL to EN