At least they have a complaint process
that can be used electronically. When Adobe gave my custom email address to a pron-spammer, less than an hour after I registered one of their products, I found that the only way to file a complaint was via paper mail sent to a legal firm care of a P.O. Box in Los Angeles, Note that when faced with this sort of thing it is recommended to send such mail "Certified, return-receipt-requested" or it will somehow be lost in transit, unlike the tsunami of physical spam I regularly receive. Clearly the Post Office is much more careful with Bulk mail than first-class.
Of course, I have no doubt Plusnet simply ignores complaints, but Adobe makes it abundantly clear up front that they do not want to hear from you about anything, now that the payment has cleared.