Vodacom is robbing us

Good day

I have 2 contracts with Vodacom, the 1st one i receive 500 megabytes and R60 airtime every month its a package of R39. The second one i bought a fone at Game a Samsung J4 core which was a contract of R139 per month and i get a R120 airtime. Yesterday i received a sms saying they going to debit a R210 on my account, when i call vodacom customer line they said prices have increased and they sent sms's to subscribers which i haven't receive. According to my knowledge they dont have a right to change a price that we agreed on in a contract coz what I've signed for was R139 in a month they now increasing the price without informing me. I cannot pay this bull**** of an amount that i never sign for