Router not working as per package

The Vodacom staff on Facebook have been awesome so far, but I seem to have hit a dead end with my complaint over a router that doesn't work properly. I took out a contract last week Tues (22nd Feb) for a 20 Mbps LTE router. Since then I haven't got more than 11 Mbps. I was advised by Vodacom Facebook to return the unit, which I did. In spite of the slip showing that my out of box return deadline was tomorrow, they refused to swap it, saying that it has to be sent in for testing instead. There's no point in me doing this because a local installer here who works with LTE says the router I have been given is unsuitable for our area - it's too weak. It will work well in other areas, but not where we are. So your techs will test it, see that it gets 4G and send it back. I just want to get beyond the front desk people and chat to someone who has the authority to sort this issue out, please! Otherwise it's going to be another week of travelling and talking to people who can't/won't help.