Wrong modem refuse to swop

I received my 50GB per month R699 LTE advanced contract as advertised: <br> <br> [URL Removed]<br> <br> When I arrived at home I realised that they gave me a Huawei B315 instead of the E5186 advertised. I took it back the next day and asked them to please swop it for the one advertised, I was told I signed for that modem and they cannot swop it. Well I came for the advertised deal, I should leave with it no?!