Electricity company change - overcharging

We changed companies believing the salesman - bad move!

Basically we are being overcharged by around €80 per month (We advised then twice we had installed solar panels) - We are being billed €99 a month for electricity when our useage since install and their switchover reading is minus 300 units for 2 months! When finally getting through on the phone we are told no record of this.

We are told to email attaching the solar inspection report -- which we did - we got the automated response that the email was received and would get a reply within 4 days - nothing yet a week later . there is no language issue as my wife is native Belgian and speaks and writes French perfectly

Can I legally just cancel the direct debit and refuse to pay the bills?