https://www.s-ridebike.com/s-ride-rd-m300-long.html
https://www.s-ridebike.com/s-ride-sl-m300-shimano.html
their pages say they are compatible with Shimano MTB parts....
NOW... the SL-M300C variant is SRAM, and the pull ratio of SRAM stuff is far longer than shimano MTB ratios....
https://www.s-ridebike.com/s-ride-sl-m300c-9-spd.html
i'd think you may have the M310 Rear derailleurs, originally...... and that shop owes you a big favor, right after they take back the wrong parts and sell you the proper ones..