Check with the company that the bank details you used are correct. - you'll soon know if it was a scam letter.... check your transaction record that all the details were exactly right.
Yes, check with your bank that the money went through to the correct account.
Yes, UBS can check if this was indeed a legitimate account or if you paid into a scam account.
Yes. Some institutions have several accounts, and it could be that you've properly paid into one of their accounts, but not the correct one. That's worth asking about.
This happened to us once with tax, where we'd paid in full, but without realising that our money had been deposited in the tax office's account for year n, but the bill was for year n+1. The staff were checking the n+1 account, so they couldn't see our payment. It took a while till someone explained to us that there were different accounts for each year, and then found our payment in the other account.