Telkom Internet Connectivity severely reduced

I took up a HomeOffice LTE 20GB contract with Telkom which included a Huawei Lte CPE B593 router, I connected this up and experienced a wonderful 19.1 Mbps download speed. However over the last several months the speed has been reducing to the point where it is no longer effective at all. My current down load speed is 1.3 Mbps. Every time I phone Telkom they log an item, but nothing changes and the download speed just keeps getting worse. So I call again, they log something, but nothing happens and the speed keeps going down. It has reached a point where I will have to seek legal advice to have the contract ended due to breech of service, then I can find a ISP that keeps their bandwidth at a steady or improving level. I have had two back surgeries and therefore there are times I have to work from home on my Laptop but the speed has deteriated to the point where this is no longer practical