Momentum Health lairs

my wife went for an eye checkup - gotten the authorization number for approval to the optometrist - after the visit all went well although she had to get glasses all good. now the optometrist says that momentum had to pay R900.00 towards the glasses, well they never paid and we sit now with the bill, Momentum claims they will not pay any amount. on the phone lady claimed they do all payments month end. yet nothing....