Account sent to the wrong person.

I received an account from ER Consulting in September for a treatment for someone I don't even know, but with the same initial and surname as me, treated at a hospital in Johannesburg. I live in Cape Town and have never been to Sandton Clinic. I contacted ER Consultants to inform them that they had obviously made a mistake. The persons name and medical aid number is not even mine. They apologised and promised to rectify, but kept on harassing me with the account through emails and SMS and now have handed me over to debt collectors.