Product: Credit card or prepaid card

The account I have offers interest free financing for a specific period of time. I also have another promotional offer in which I'm paying 10 % for a period of time on a purchase thus two plans currently. The interest free was for a period of 6 months from the date of purchase. 

The purchase for the 6 month interest free promotion was done XX/XX/19 in the amount of {$700.00}. The first payment made was for {$280.00} on XX/XX/19. The statement reflected a min payment of {$150.00}. When I looked at the statement from XXXX regarding how the payment was applied only {$8.00} went towards the 6 month interest free promotion with the majority going towards the plan at 10 %. 

I emailed the company XXXX/XXXX/19 asking for the minimum amount to be applied to the 10 % and the remainder to go towards the 6 month interest free ( I was trying to amortize the {$700.00} over 6 months so it would be completely paid off by then ). This was done XX/XX/19. It was advised that they apply payments to those with the highest balances and only put money towards the promotional plans that expire within the next 2 months. I know the game they are playing hoping people default on the interest free plan so they can back charge interest. While that is legal and fine, that was not my intent when making the payment. 

I then responded again asking for the payment to be reapplied so that the minimum would go towards the 10 % rate and the reminder of the payment be applied towards the promotional 6 month interest free plan. I was sent the same copy and past from the prior email which didn't resolve the issue. 

I proceeded to then call. At this point I had made two payments and neither had been applied the way I had requested. I was told by that rep they would fix the payments and would be taken care of. I stated I wanted all future payments to be applied this same way. 

I get the next statement and its showing only one payment was adjusted and now I've had 3 applied within only 1 ever getting applied the way I asked for it. 

I then call the company again. I was told I needed to talk to a supervisor given how long this was going on for. The supervisor was the least helpful person I've ever talked to. I was told that " it clearly states on page 3 of the statement if you want payments applied a specific way how to request. '' This information is no where to be found. The only thing it states is how to avoid interest and to call. I was then told by the supervisor that because it had been more than one billing statement I'd have to write a letter to explain what I wanted done. 

I had already requested this in writing via email back on XX/XX/19 asking for this. I was told I'd have to write a letter and my statement clearly explains where to send it on page 3. This information is no where to be found on page 3. The only thing it says is on page 2 stating if you think there is an error on the statement. 

I explained that I had also called and only one was adjusted. The supervisor said I would have had to put in writing for the prior payment. Again the rep I spoke to at that time never told me that. Also the supervisor refused to do anything because " she didn't want to get it wrong ''. 

The supervisor also stated that if I want payments applied a certain way I have to call in each month to get it adjusted correctly and that " several customer have to do this ''. Again, this is no where explained on the statement nor when you make the purchase explained you have to do this or how payments are applied to the promotional items.