Terrible service delivery on lte deals

In November of last year we where told to come into the store to renew our lte data plan contract that consist of a Sim and pocket modem. We renewed the Sim plan to 20gig day and night surfer as of the 2/01/24 we are unable to surf the internet properly without the reception continously going down and picking up again yet to go back down within half a second. Why should we be paying for a data plan that we cannot even use. Upon a visit to the chatsworth centre store we where told that there is a problem but no particular time frame is given in regards to fixing this issue we run a small business from home and we require data seeing as it's a means of income and this is very very unprofessional how can you be paying for something that you cannot use.