Credit Card Mayhem

This bank's staff don't seem to understand the difference between a statement date and a billing date! Late last year FNB unilaterally changed my statement date (which closes off a month) from the 4th to the 5th. I brought this to their attention and requested them to ensure that it is returned to the 4th for future statements. Instead they change my payment date (the date that they bill me and deduct the amount from my cheque account) to the 4th. This of course automatically affected my statement date. After much to-ing and fro-ing, they stated that it was corrected but then in early December they changed the amount payable from full to minimum thereby invoking an interest which they subsequently reversed after I complained. Now this month (January) they again changed my billing date to the 4th thereby once again affecting my statement date. This effectively means that the "new" month will NOT start on the 5th but sometime later thus seriously impacting on my budget! After many emails to this effect, it still seems that the credit card division is clueless as to what "Billing" and "Statement" means. Perhaps their management can contact me so that I can explain to someone who can help me?