You should contact the parking company and explain you did pay. In terms of this situation, where you go from here depends on the type of parking fine you initially received. There are two, that could be possible in this scenario:
a Penalty Charge Notice (PCN) or an Excess Charge Notice (ECN) – usually issued by the council on public land, such as a high street or council car park
a Parking Charge Notice – issued by a landowner or parking company on private land, such as a supermarket car park
If it is a ECN the steps, are as follows:
You’ll be sent a letter and a form called a ‘notice to owner’. Don't be put off if the letter sounds final – you still have 28 days to make a formal appeal, called ‘making formal representations’. It’s free to appeal and the notice to owner will tell you how.
You can usually get a 50% discount if you pay soon after your informal appeal is rejected. It's a good idea to pay at this point if the council have a strong reason for objecting your appeal. If you don’t appeal and don’t pay within 28 days, the penalty will go up by another 50%.
If your formal appeal's rejected, you’ll be sent a letter called a ‘notice of rejection’. You can challenge the council’s decision at an independent tribunal. It’s free to do and you don’t have to go to the tribunal – you can submit your reasons and evidence in writing. Appeal online on the website of the Traffic Penalty Tribunal (outside London): https://www.trafficpenaltytribunal.gov.uk/ or London Tribunals (in London): https://www.londontribunals.gov.uk/
If it is a PCN:
Check the British Parking Association (BPA): https://www.britishparking.co.uk/BPA-Approved-Operators or International Parking Community (IPC) websites: http://www.theipc.info/aos-members to see if a parking company is a member of an ATA.
If the parking company isn’t an ATA member, there’s no formal appeals process but there are other things you can do.
If the parking company is an ATA member, you can appeal to an independent appeals service. It’s free to do, so it’s worth trying if you still think your ticket was unfair. They might see things differently to the parking company and agree that your ticket should be cancelled.
The way to appeal will depend on if the parking company that gave you the ticket is a member of the BPA or IPC approved operators scheme. Make a formal appeal to Parking on Private Land Appeals (POPLA): https://www.popla.co.uk/ if they’re a BPA parking company. If they’re an IPC member, make a formal appeal to the Independent Appeals Service: https://www.theias.org/appeal
For a ticket from a BPA member, you have 28 days from when your informal appeal was rejected to make a formal appeal.
For a ticket from an IPC member, you can make a formal appeal for free within 21 days. After 21 days, you can still appeal within 1 year of your formal appeal being rejected if you pay a £15 fee.
Make sure you include any evidence that will support your case. I trust this assists