Unfortunately the issue is not with buying the gift cards, it is then using the gift cards yourself to apply another discount to goods from your employer. I can see why you're being investigated for gross misconduct and this is why you have been suspended. If they accept you were truly naive in not realising that applying a double discount to goods through this loophole was wrong then you may avoid dismissal and end up with a final written warning...however and I can't stress this enough, there is a real risk you will be dismissed for gross misconduct attributed to theft from the company. This will have a potentially significant impact on you gaining future employment in the short term. I would, if you are able, consider finding alternative employment and resigning prior to any disciplinary action...it will depend on how easy another job is to find, your position in the company and whether you have suitable union representation, but I would seriously consider my options here, if I were you.