Handed over to debt collectors without knowledge of debt

I hadn’t been using my rain SIM card for years, there was no communication from there. Years later in 2023 I got a call from debt collectors telling me that my rain account was handed over to them. Rain had made no attempts of informing me that I owed them money. What was meant to be month to month, no contract obligation ended up with me dealing with collectors. I was told that the first ever payment I made was for the service, and that I still owed them initial fees. I don’t have a problem paying my dues, what upsets me is that I wasn’t told about it by rain, but instead I was handed over. My profession requires that I have clean credit, but now here I am handed over to debt collectors over something I knew nothing about. The least that they could have done was to drop me an email telling that I owe them.