Another unit of my employer being unethical

I work for a financial company that also has a small banking business (small part of the business but it is a federally regulated institution), where I have two bank accounts. They were offering a promotional interest rate on an account so I opened a second account and a fair chunk of my savings in it. I realised that transactional capabilities were limited so moved some money over the course of a few days (due to account limits) to a couple of external bank accounts so I could access it easily (majority of funds remained in this account).

I recently realised that they weren’t giving me the promo rate even though I was getting communications that they were and the online banking page for my account shows the promo rate. I called to ask them. First they said it was because I had moved the money from an existing account at the same bank, which is not allowed. I pointed out that the T&C say the money shouldn’t have been in an existing account as of a certain date and mine wasn’t. Then they said they’d exercised their right to deny anyone they choose the rate based on suspicious activity (which they said the transfers out of the account were). This seems a reach. T&C just say that the interest won’t be applied to transferred funds. And they never communicated to me that my account was deemed ineligible. They went so far as to repeatedly tell me I was getting the promo rate.

This seems unethical to me, and an effort to intentionally mislead people on the assumption that they may not realise they’re being shortchanged. The change in reasons also indicates they’re scrambling to cover their tracks. I’m really angry and am tempted to file a complaint with the ombudsman. But I’m concerned about repercussions given this company is also my employer.

Any advice?