Double deductions from bank account

I have been a loyal customer of MTN for years. End of May MTN deducted my contract amount from my account. On 4 June, they tried to deduct again. They blocked my numbers because of non-payment after the 4th. They have tried numerous times during June to deduct again - every time I have to pay bank fees. After very long phone calls, I am still not unlocked and no one can tell me why they are making extra deductions.