You can't have two Apple IDs associated with an iPhone, although you can use both from the iPhone. As you indicate, the charge is being made on the associated Apple ID for one reason or another, the one you don't want the charge on. Since you are having a problem with a subscription, I suggest you use Subscriptions and Purchases https://support.apple.com/en-euro/billing. If you think you may be able to get a refund, then use the request a refund link. It will take you to Request a refund for apps or content that you bought from Apple https://support.apple.com/en-euro/HT204084
See How long refunds from the App Store or other Apple services take https://support.apple.com/en-us/HT210904
You also can get Apple telephone support for help in solving your problem using this link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362 Be patient; sometimes you can't get immediate telephone support.
And here is how to contact iTunes worldwide support via text or chat using this link https://support.apple.com/choose-country-region/itunes After choosing your country, see the heading Tell us how we can help.