Can't get a job thanks to Medshield

I was on Medshield and terminated my membership on the 24th Jan 2019 as I was out of work and could not afford it. I found out from a recruitment agency that I had a default on my name and it was blocking me from finding a position. When I queried the default I found that it was Medshield who blacklisted me with no prior warnings. To date I have not received a call, an email or any communication stating that my last debit order was returned so I had no clue that I owed them any money. Thanks to this, I cannot get employment because all companies do credit and ITC checks. If I had known about this I would have made an arrangement to pay because I worked so hard to get my credit score/status clean and up to date. I want answers as to why I was not contacted about this. I was informed that they sent a letter regarding this to my postal address in March but I have not received any mail in months from the Post Office. I will NEVER use Medshield again and I will tell everyone I can of the terrible service that I have received AFTER i terminated my membership!