I don't perceive the problem as "how to prohibit an ex from reclaiming your name," I perceive it as "how to stop bill collectors from calling you about debts from someone with the same last name as you."
I was in the latter situation a couple of times and was able to resolve it just by jumping through the collection agencies' bureaucratic hoops, i.e. leaving messages at the toll-free number provided saying "I'm not this person, I'm not related to this person, and it's not my bill," and ultimately saying the same thing to a live human. I had to be somewhat firm about politely declining when they kept doing a little social-engineering-type fishing ("do you have any information that would help us locate this person?").
Annual income twenty pounds, annual expenditure nineteen nineteen and six, result happiness; Annual income twenty pounds, annual expenditure twenty pounds ought and six, result misery.