NOT HAPPY WITH VODACOM SERVICE

I am gatvol with Vodacom , since this year has started every month I have calling them complaining about my bill . In Feb I wanted to cancel my contact with them because the bill has different amount from R440 to almost R800 .I was assisted by Thabiso Thanane who convinced me to downgrade and take P20lite for R195,i will receive 2 gig for 24 months and 10gig for free for 6 months big mistake I made because I have been paying R354.89 for that phone instead of the R195 which was sold to me . I have 2 contracts phones with Vodacom I used to pay R440 .00 for both phones now since the so called downgrade the bill has increased i pay close to R600 I have called and even cancelled insurance to decrease the monthly instalment

On the 10/04/2019 I called Vodacom regarding me debit order which is high I spoke to Ntsidiseng Ditlokwe I asked her why was I paying R289.49 for device which is R195, she advised its because of insurance after the call I contacted the voda insurance department to cancel insurance i was assisted by Sibongile Dlamini who confirmed it will be cancelled .... today i receive as invoice which i am now quoted R354 8 9 for the P20 lite which is suppose to be R195 , now for both phones i will be paying R592.64 i am not even sure which amount will i be paying next month . I am extremely annoyed i wish i cancelled this contact and never listened to Thabiso . I want to understand why is my bill different every month ?