Vodacom blaclisted my MTN phone

I have been an MTN customer from the day my mum purchased a contract with Al-tech in 2012. Since my return from Bali I was unable to access my MTN network. I have contacted Al-tech, who did some minor troubleshooting on the MTN SIM card and had identified that the SIM was fine but the Phone needed to get repairs from Samsung. At the Samsung store, I was requested to call MTN to find out if the phone was blacklisted prior to them taking the phone in for repairs. MTN confirmed this, but requested that I call Altech to find out why. Altech identified that Vodacom had blacklisted my IMEI the day I had left for Bali. I visited the Vodacom store today and filled in a 'request to unblacklist document'. The lady at Vodacom was swift and helpful, although this process took 7hrs of my working time. How on earth did Vodacom get access to blacklist my MTN phone? This is the second and only complaint I have logged on this platform, and both instances relate to Vodacom?!