Vodacom - lackluster internet experience. started out good but now not so much...

I got the 400/400gb LTE deal last year November for Black Friday - Initially I was very happy with the service and everything was going well but I've noticed a very substantial decline in the quality of the internet I'm paying for. It has now been roughly 5 months of usage and I can hardly watch Youtube videos on 240p if someone else in the house is using the internet aswell. The only reason I'm giving a lackluster review is because this is a 24 month contract and I still have 19 months to go which makes me worried what kind of internet I'll be getting in the next 5 months. 400gb is not much good to anyone if you cant even open a facebook page - really is a bit pointless and a waste of money.