I am angry and disappointed at this company

My company has a prepaid 3 lines account with lanline and it was all good when we started but the lines are giving us issues , sometimes only 2 lines work and other times only 1 line works and we ended up loosing business because of that, we have been complaining to lanline about that and this issue has been going on since last year, their technicians came twice to our office , and everytime they come to the office they change the simcards then after a day or 2 the same problem reoccurs , It feels like this guys don't understand their product because they can't even fix their lines