Complaint sub-issue: Charged too much interest

I received an email promotion from BBVA Credit Card on XXXX for 0 % on all purchases from XXXX to XXXX for 6 billing cycles. The offer had to be activated by XXXX which I did. During XX/XX/2021 I charged approximately {$3800.00} on the 0 % offer. 
My XXXX XXXX statement showed purchases of {$1900.00}, not all of which was charged in XXXX as I understood the offer to cover. I paid my prior balance of {$1200.00} in full prior to the due date of XXXX. That statement showed NO INTEREST charges and NO PROMO balance. 
My XXXX XXXX statement showed purchases of {$3700.00}, of which all but {$770.00} was charged in XXXX, I was however charged {$3.00} in interest on BBVA 's purchase balance of {$180.00}. My promo balance was {$3100.00}. On XXXX I called BBVA to reverse the interest charge and given ticket # XXXX to confirm the reversal. To cover the non-XXXX charged + extra I made a payment of {$1100.00} on XXXX. 
My XXXX XXXX statement showed purchases of {$1700.00}. I had paid in full ALL charged NOT covered by the 0 % interest offer, but I was charged {$19.00} in interest and the {$3.00} prior interest was NOT credited. BBVA showed a purchase balance of {$910.00} and a promo balance of {$3400.00}. I called BBVA again for 1 hour on XXXX, finally speaking with Supervisor XXXX to reverse ALL interest charge. She did not understand why I was being charged interest but didnt give me a ticket #. I made 2 payments totaling {$1700.00} prior to the due date to cover my new charges to insure NO MORE interest charges in the XXXX statement. 
My XXXX XXXX statement showed purchases of {$370.00}. I was again charged interest, this time {$21.00} and NONE of the prior interest was credited. BBVA showed a purchase balance of {$1000.00} and a promo balance of {$3200.00}. BBVA was obviously applying my new purchase payments to my PROMO purchases which were 0 % interest until XXXX. I spoke with a BBVA supervisor, XXXX XXXX, emp. # XXXX, on XXXX who confirmed payments were going to the 0 % purchases because I had not called BBVA to specify where to apply my payments. He also told me to call BBVA 's CS # XXXX as BBVA has NO BILLING dept. and tell them how much and when I was making a payment and to apply it to my new XXXX purchases of {$370.00}. I did, saying I was making a {$400.00} payment on XXXX to be applied to my new purchases FIRST. He gave me ticket # XXXX and said he would have ALL interest reversed and call me by XXXX to confirm all was correct. I received no call. 
I did get my XXXX XXXX statement showing {$14.00} in new purchases, {$3.00} in new interest, a purchase balance of {$180.00}, and a promo balance of {$2900.00}. I have NO idea where they are getting their figures. I called BBVA again today. I spoke with Supervisor XXXX in XXXX, who saw all the notes and told me the charges were valid and wouldn't be reversed. I asked him who regulated BBVA. He didn't know, but gave me their legal dept #. 3 calls later and on hold for 10 minutes I was told to contact the Consumer Financial Protection Bureau. I did and was directed to this site to file this complaint. 
I believe BBVA to be making fraudulent promotions of 0 % interest rates they have no intention of honoring. In addition, a week later I received another promotion offer of 10 % back on all purchases made during XXXX up to {$50.00}. THAT encouraged me to charge more with BBVA than I normally would have as I didn't really need the 0 %. I did receive that credit on XXXX which {$1.00} more than the {$48.00} I have been charged in interest so far in BBVA 's 0 % promotion. When I add in the HOURS I've spent trying to understand, correct, and finally discovering BBVA 's false promotion, I lost WAY MORE THAN {$48.00} IN INTEREST. BBVA owes me much more and should be investigated for their actions. Thank you. 
PS My account # changed from ending in XXXX to ending in XXXX in XX/XX/2021.