internet line not up to speed

Very frustrated with Telkom !!! I took a 10mbps line on their lockdown special but im only getting 4mbps which goes as low as 2mbps I spoke to 4 people who either tell me they escalated my issue to tech department or i must call again and speak to the tech department or contact openserve who installed the line If im not able to get the line speed im told i should be getting why should i pay for it ?? and nobody is willing to downgrade my line Asked on FB,email on their website and the app but still no one responds once again Telkom has proven to be useless