You sound very irrational going into the store with the equipment.
Read your contract. You need to give a month's notice and cancel in writing. No point visiting the store or phoning people (although it is easy enough to dial 1901 and choose the option to cancel).
To give notice and cancel in writing you can post a letter to Eir, or by using this form: https://www.eir.ie/support/online-forms/cancellations/
After cancellation they will send you a letter with instructions on how to return your equipment.
If you are in a contract period and you cancel your final bill will include an early termination charge.
Comreg may assist but customers have to follow processes, Comreg have clamped down on babysitting customers and will want proof of attempts to rectify problems with their providers. Email, Email, Email, can't be ignored or hidden and will act as proof of attempts to rectify issues etc.
OP, Retail staff have enough S&€TE to deal with, with Covid-19 protocols.
For the record, I don't work for Eir but did for another network