I set it it up by clicking the link at the end of the filing process. I now have a letter saying that I need to pay it now. I don't have that kind of money, that's why I set up the payment plan.
If the IRS is not acknowledging the installment payment request you may or may not have already made then you can apply for one now ... the bill they sent should have tell you how ... https://www.irs.gov/payments/online-payment-agreement-application
The only way to get an IRS approved payment plan is to apply directly to the IRS. There is a non-refundable application fee. Many payment plans are approved instantly if you apply online.
https://www.irs.gov/payments/payment-plans-installment-agreements
https://www.taxpayeradvocate.irs.gov/get-help/paying-taxes/installment-agreements/
It is possible to apply for a payment plan indirectly, using another company, but the application fees are higher and the company applies for you by mail, which takes much longer to get approved.
Is there a chance you actually applied for some kind of loan program where the company pays the tax with a loan and you pay the company back? (I'm sure the interest and fees will be much higher than a direct IRS payment plan.)
I have no knowledge if the company you used is good or bad, but for the other reasons I mentioned, I would never use a private company to request a payment plan, I would only apply online directly to the IRS. That's assuming you want to pay your taxes in full eventually. If you want to negotiate a lower payment (offer in compromise), I would work with a local tax professional, not a national or online company.