Bad service received from various staff

I saw the 30% sale was only running until today and thought I would spoil myself with new gym tekkies . You have a board stating to ask for assistance with sizes, after I had to go find someone to help me they just checked the few boxes in one of the shelves and told me you don't stock my size in that specific shoe without checking in the storeroom. After deciding on a different shoe and queuing to pay we noticed that there was only one cashier working. Paid my shoes and about to leave the store the security beam goes off and the security grabs my package and start checking what I bought is well on the slip. People entering and leaving the store are all staring at this situation as it looks like we were *****ing. Highly unprofessional and no communication the security goes through the package and takes out a tag that was left behind by the cashier. So embarrassed we asked to see a manager and was told the branch manager is off on Sundays. A department manager comes closer to assist in telling us that this is the procedure that they must follow. Why not communicate to the customer what you will be doing and why do this at the entrance of the store for everyone to see?