Terrible accounts service and feedback

This morning at 7.50am I received a call from a debt collection agency stating I owe an account to Lab24. Needless to say I was concerned. When I contacted Lab24 and requested a statement or invoice I was told the account was from May 2019. Prior to the phone call from the debt collection agency I had received 2sms in July and August-i had assumed these were **** SMS because we hadn't been to the doctor in ages. From May 2019 until today I had NO correspondence from Lab24 of this existing account. When I questioned the account department at Lab24 they blamed it on the back log due to COVID. And went as far to say a status will be put on my profile at the credit bureau if I don't pay. I was told this is prescribed debt-after 36 months I do not need to pay if I was not informed of the debt. When I had asked to speak to a supervisor apparently they will be unavailable until next week. Highly frustrating and disappointing and extremely poor service.