Sameo is correct. See if a new tensioner was included in the price you paid. If it was, I suspect you paid for it and didn’t get it. They come with a kit from Autozone or the dealer at a higher cost. They should also have suggested a new water pump as 9/10 of the labor to install the pump is already done when they have the timing belt off.
To my thinking there is no way the timing belt should have slipped a cog or two if the job were done properly. They owe you a fix as the valves were not bent when you drove it in the first time. You did DRIVE it in didn’t you?